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Item Studies on the reproductive performance of dairy cows in New Zealand and some factors which may influence reproductive efficiency : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy at Massey University(Massey University, 1990) Chaimongkol, ChockchaiThis thesis is comprised of a series of studies on aspects of the reproductive performance of dairy cows in New Zealand. The studies of ovarian activity in post-partum dairy cows by ultrasound examinations were conducted in a spring- and an autumn-calving herd. This study showed that there is seasonal variation in the initiation of post-partum ovarian function in dairy cows in New Zealand, and this influences some aspects of reproduction. The interval from calving to the first post-partum ovulation in the autumn-calving herd was significantly shorter than that in the spring calving herd. Other reproductive indices were shorter in the spring-calving herd. The mean milk progesterone concentration during the dioestrous phase(Day 7-16) of the normal first cycle for cows in the spring-calving herd was significantly higher than in animals in the autumn-calving herd. In addition, the mean number of follicles in each of the follicle-size categories from 11 days before the first ovulation in spring-calving cows was significantly higher than in autumn-calving cows. There were three wave-like patterns in the mean size of the largest follicle during the first normal cycle. The patterns of the mean number of each follicle category and the mean size of the largest follicle in cows which had a shortened first cycle were similar to those seen in the first two stages of a normal first cycle. The follicular patterns in cows which had a short first cycle were also the same as those in the first stage of a normal first cycle. The use of gonadotrophin releasing hormone(GnRH) in post-partum anoestrous dairy cows in a spring-calving herd showed that the GnRH injection could induce luteinising hormone(LH) release and ovulations The study of ovarian activity post-injection showed that the GnRH-induced LH release was associated with an increase in average number of medium follicles(MF's) and a decrease in large follicles(LF's) in the ovaries of treated cows. Treated cows ovulated 4.7±2.6 days post-injection, while only one control cow ovulated on the equivalent of Day 5 post-injection. The reproductive indices in treated cows were improved, compared with untreated controls. Oestrous behaviour was studied in a group of sixteen Taurindicus heifers(Sahiwalx Holstein Friesian crossbreds)after oestrus synchronisation treatment by using a CIDR {Control Intravaginal Drug Release) device. It was found that these animals preferred to be mounted rather than to mount when in oestrus. The mean interval from CIDR removal to the onset of oestrus was 31.5±2.3 h, with the mean duration of oestrus(8.3±1.9 h). The use of visual observation in combination with tailpaint scoring could detect all oestrous animals. The DairyMAN programme was used to analyse breeding records from two intensively managed research dairy herds. Results from analyses produced by the programme were used to monitor and compare against standard or target values. The results showed that reproductive performance in the two herds was above target values. The increase in the use of hormonal treatment such as prostaglandin F2α to synchronise oestrus and/or to increase fertility of a herd, concomitantly with improvement in oestrus detection efficiency, resulted in an increase in submission rates and conception rates in these herds. Nutritional supply before and after calving can reduce reproductive performance of a herd. Relatively low reproductive performances were obtained in both herds during the 1985 season in which pasture growth was badly affected by climatic conditions. This was reflected in the lower occurrence of +PMH(behavioural oestrus events recorded before the mating period commences) in the No2 herd in 1985(61%), compared with a target value of 85%, whereas the average of all 7 years was 80%. The conception rates of the herd were also affected as the first service pregnancy rate(PR) was only 43%, compared with a target value of 59%. The average of all 7 years was 56%. Relatively high reproductive performance was obtained in 1986. The submission rates(SR) at 3 and 4 weeks after Planned Start of Mating(PSM) were 94 and 100%, respectively, compared with target values of 90 and 100%, respectively. In addition, the occurrence of +PMH was high in 1986(90%), compared with a target value of 85% and an average of all 7 years(80%). The first service PR was also high in 1986(71%). The proportional incidences of short return to service intervals(1-17 days) were high(32 to 57%) in the No1 herd which used natural mating, compared with 6 to 22% in the No2 herd which used artificial insemination.Item Studies on the use of the CIDR intravaginal device for reproductive management of dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy at Massey University(Massey University, 1990) Dick, Alberto RaulThis study was undertaken as a series of projects which involved selected studies with the CIDR Controlled internal drug releasing device (Eazi-Breed CIDRtm-B, Carter Holt Harvey Plastic Products, Hamilton, N.Z. intravaginal device in dairy cattle. In the first project, a CIDR device was inserted at different stages of the oestrous cycle to characterize the dynamic changes of the follicles in the ovaries of cycling cows, the associated changes in plasma progesterone concentrations (PPC), and the effects of progesterone from the device on cycle lengths. The results demonstrated that the progesterone released by the CIDR appeared to enhance the development and maintenance of a dominant follicle. The reproductive responses after device removal were influenced by the follicular population, and by the stage of the follicular wave even in the absence of a corpus luteum (CL) The PPCs during CIDR insertion or after removal were influenced by the type of animal and the stage of the cycle when treatment was initiated. The stage of the oestrous cycle in which the device was inserted also influenced the average cycle length. In the second project, the tailpainting and raddle technique combined with scoring and re-raddling gave a precise correlation with visual oestrus detection and with patterns in the onset of oestrus in groups of heifers and cows after different synchrony treatments. The average interval to oestrus was concentrated between 30 and 120 h after using different treatments for oestrus synchronization. In the third project, a controlled breeding programme for cows in herds with a daily milk quota was investigated, with a view to improving reproductive performance through the strategic use of the CIDR intravaginal device. The study showed that the mean interval from Planned Start of Mating (PSM) to first insemination was shorter in all treated groups in year-round herds, and treated cows had fewer days open than control. Conception rate to first insemination differed statistically between groups, but not for second inseminations. As a consequence, the mean number of services per conception also differed significantly between groups. Oestrous responses in all farms differed significantly in the treatment group compared with the control group (76% vs 63%; P< 0.001, respectively). The return to oestrus in treated cows was synchronized in 85% of non-pregnant cows on days 22 to 25 after first insemination. The average responses to the two doses of prostaglandin at CIDR removal was similar for half dose vs full dose (72% vs 68%, respectively). However, this management advantage was partly lost because of lower fertility and because of mistakes relating to the interpretation of the tailpainting system which were frequently made by the owners. In the fourth project, the effectiveness of using a milk progesterone test to identify non-pregnant animals and consequently to improve oestrus detection rates was evaluated in a management system for dairy cows involving the use of CIDR devices for controlling return to service intervals. The average percentage of non-pregnant cows inseminated during the second period of artificial insemination (AI) was 63% and varied from 44% to 77.2% among individual herds. In general, the study showed that the identification of non-pregnant animals did not improve the percentage of animals inseminated over the second period of AI. In the last project, the dynamic changes of follicles on the ovaries at two different post-partum periods was characterized as well as the post-treatment response rates in oestrus and ovulation in anoestrous dairy cows. The population of follicles in classes 1 (<6 mm), 2 (6 to 9 mm) and 3 (>9 mm) varied between cows in both post-partum periods, but the average number of follicles did not differ significantly between day 25 (early) and 50-55 (late) for treatment and control groups. In the late post-partum period, the average number of class 1 follicles increased in the animals of the treated groups (P< 0.05), and when the comparison in treatment groups was made between early and late post-partum period, the average number of class 2 follicles and the total number of follicles were both increased at CIDR removal (P< 0.05; P< 0.01, respectively). The average number of class 1 follicles in the early post-partum period increased significantly in the treatment group irrespective of whether or not animals displayed oestrus or ovulated with CL formation after treatment with CIDR/PMSG. The diameter of the largest unovulated luteinized follicle in treated cows which displayed oestrus and/or ovulated increased significantly during CIDR treatment, and its growth continued after the device was removed. In both post-partum periods, normal and luteinized class 3 follicles were found in non-cycling cows, where some had large normal and others had large luteinized follicles. Only 25% and 33.3% of the treated cows in the early and late post-partum period displayed oestrus, respectively. However, 55% and 50% of the treated and control cows which had not displayed oestrus, actually ovulated and formed a CL in the early post-partum period. From the results of this study, one can conclude that although insertion of a CIDR device into cycling cows synchronizes oestrus, there remains significant variation among animals in the precise time after device removal that oestrus commences. Moreover, some animals have reduced fertility at the synchronized oestrus. To overcome these two limitations on the benefits of synchronization, the duration of treatment programmes based on a progestagen will have to be adjusted to obtain high conception rates, and greater account will have to be taken of follicle wave patterns as a factor influencing precision of synchrony. These considerations apply also to the re-use of CIDRs after insemination, to reduce variation in return to oestrus and to improve fertility in cows which do not conceive to insemination at the first synchronized oestrus. To ensure precise synchrony it is important to emphasize that the most common problem in breeding management in dairy cows is inadequate oestrus detection. The tailpainting system may be less satisfactory in herds with continuous calving patterns. It shows particular potential for further studies between animals which may not display oestrus, and the associations of the tailpaint and raddle technique in animals with different coats and skeletal conformation. In non-cycling cows, further studies have to be focused on the importance of identifying factors which affect the treatment response, the endocrinological characteristics of these animals, and the interactions of the nutritional status, body condition and ovarian function during the post-partum period.Item Some aspects of growth rate as it is related to reproductive efficiency in dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Science at Massey University(Massey University, 1979) Tan, Kim SingThe purpose of the study reported in this thesis was to evaluate whether liveweight, measured in Friesian yearlings immediately before the breeding season commenced and in parous cows of the same breed just beforecalving for the herd began, was related to reproductive performance during the first four weeks of the mating period. Should such a relationship be confirmed 'target weights' which would ensure a high level of reproductive efficiency could be established for animals of this breed under normal husbandry conditions in New Zealand. A pre-requisite to the investigation was thatthe method(s) used should be easily applied in a commercial farming situation. Body weight measurements for 184 yearlings (5 herds) and 288 parous cows (4 herds) which were at least three-quarter bred Friesian were taken at the times indicated above and related to submission rates (S.R.) and pregnancy rates (P.R.) during the first four weeks of the following breeding season. The cows were bred by artificial insemination with heat checks being made by experienced stock men; yearlings were mated to young bulls fitted with chin ball mating harnesses. P.R. and the dates of conception were confirmed by both pregnancy examinations at the conclusion of the breeding period and by subsequent calving information. Reproductive performance in the yearling heifers was high with S.R. averaging 94% (range 88-100%) and P.R. 86% (range 71-100%) for the five herds. The majority of the heifers were judged to be in good body condition with mean body weights for the herds ranging between 231±27 and 277±22 kg (mean ± S.D.). Differences in liveweight between herds were probably related to management during rearing although age variation and minor differences in the amount of Friesian 'blood' in each herd could have been contributing factors. When individual herd effects were removed a positive but non-significant linear relationship between liveweight and S.R. was achieved with the yearlings. From the six points plotted on the regression it was noted that the lightest group of animals had a submission rate of 76% whereas all other groups had submission rates in excess of 94% thus suggesting a threshold effect. The minimum liveweights for the lightest yearling groups exceeding a 90% submission rate varied from 204-229 kg depending on the herd. While a positive relationship between liveweight and pregnancy rate was noted in the yearling data this was neither linear nor significant - further investigations seem warranted to resolve this particular issue because of its importance in breeding management. The significant differences noted between herds in yearling pregnancy rates may have been due to differences in fertility of the bulls used. The reproductive performance of the three year-old and mature age groups of parous cows was satisfactory (S.R. averaged 87 and 86% and P.R. 69 and 65% respectively) but that of the two year-old cattle poor (S.R. 67% and P.R. 56%). Marked differences occurred between herds. Apart from the possible influence of liveweight before calving on these parameters of performance analysis of the reasons for herd differences was beyond the scope of this study and not attempted. Differences in liveweight of the different age groups of cows both within and between herds was marked and, apart from the relationship with age, could most likely be attributed to management during the late autumn and winter period before calving began. Any association between liveweight and subsequent reproductive performance was however generally poor and inconsistent and in retrospect it was concluded that the method that had been used for investigating any possible relationship was unsatisfactory. A future investigation in which variables are more effectively controlled has been suggested. Two year-old heifers experiencing their first lactation continue to be a problem group particularly under New Zealand dairy husbandry conditions. Careful management commencing during rearing and extending through first mating, calving and second breeding is required if a high level of reproductive efficiency in this age group is to be achieved.Item Production characteristics and responses to feeding by Friesian cows fat and thin at calving of high and low genetic merit : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University(Massey University, 1984) Ngarmsak, SupachaiA review of literature is given on herbage intake achieved by grazing lactating dairy cows. The lactating cows have higher herbage intake than non-lactating cows. Condition at calving may have an effect on herbage intake by dairy cows. The theory of response, the response to feeding both before and after calving are also reviewed. The literature is reviewed which discusses responses to feeding in Europe (where diet of the cows are mainly concentrates) and in Australia and New Zealand where dairy cows graze mainly on pasture. The evidences of improving cows quality by selection are given with special emphasis on New Zealand dairy cows. Genetic merit of a New Zealand cow for milkfat production is measured by her breeding index (BI). The main objective of the work was to study production characteristics and response to feeding in early lactation by Friesian cows, fat and thin at calving, of high and low genetic merit. Over lactation High BI cows produced more than Low BI cows. The differences between BI groups in milkfat production was in close agreement with the expected differences based on BI's. High BI cows had slightly higher herbage intake than Low BI cows but no signifcant differences were found. Low BI cows were fatter than High BI cows. No significant difference in fatty acid composition of milk between the BI groups was found. Over lactation Fat cows produced more milkfat than Thin cows. Improving 1 condition score at calving was associated with an increase of 10.5 kg milkfat. No significant differences in response to feeding in early lactation between High BI and Low BI cows nor between Fat and Thin cows were found. The response to moderate underfeeding during early lactation was mainly immediate response. The residual effects of underfeeding were small and confined to 2 weeks after returning to full feeding. Underfeeding significantly increased mole % of long chain fatty acids of milk and significantly decreased mole % of short chain fatty acids.Item The development of an expert system for diagnosing reproductive problems in seasonal dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University(Massey University, 1997) Hayes, DavidAn expert system for investigating the reproductive performance of seasonally calving dairy herds (DairyFIX) was designed and developed. The system uses information retrieved from an on-farm information system (DairyMAN) to identify the primary causes of reduced performance and make recommendations for further action. The current performance of DairyMAN user herds and a sample of herds from the National Dairy Database were initially measured. Realistic targets for each performance indicator were then calculated using this information. The associations and interactions between the performance and diagnostic indicators used in DairyMAN were more clearly defined using multivariate statistical analyses and path models. Additional information was obtained from the literature for incorporation into the DairyFIX system. The reproductive performance studies covered one complete year (1993/94 season) and were limited to spring calving seasonal herds which are typical of the New Zealand dairy industry. Such herds are managed so that all cows calve on a synchronous annual cycle as close as possible to the "ideal" calving date in that location. A typical aim is to have calvings spread over 6 to 8 weeks with a narrow spread being strongly favoured. The herd planned start of calving (PSC) date defines the beginning of this optimal period of calving and the planned start of mating (PSM) the first day of mating that must be used to achieve the desired calving pattern. Expert system development is introduced in Chapter 1 with some historical information that supports the use of on-farm information systems. The concepts and design methods used for developing expert systems are then reviewed in brief. Examples are provided to illustrate the different levels of sophistication that can be used for developing expert systems. These demonstrate that relatively simple designs are often the most successful. Examples including Bovid and Dairy Expert are discussed in detail. The methods used to monitor seasonally calving dairy herds are then reviewed with an emphasis on the main performance and diagnostic indicators used in DairyMAN. These include the four and eight week calving rates, 21 day submission rates, non-return and conceptions rates and four and eight week in-calf rates. Empty rates can be considered the final definitive measure of performance by many dairy farmers, but the difficulties with interpreting this figure are presented. The limited mating period in seasonally calving dairy herds means that the assessment of heat detection is difficult and often inaccurate. For this reason several alternative methods for assessing heat detection efficiency and accuracy are discussed in detail. A detailed description is given in Chapter 2 of herd and individual cow performance for DairyMAN user herds and the National Dairy Database sample. These data show that the reproductive performance of New Zealand herds is often below that previously reported. Calving rates are on average above industry targets, but only with a significant level of calving induction. Removal of inductions for welfare and marketing reasons will have a significant effect on the performance of many herds. Submission rates are the earliest available measures of performance during a mating season. New Zealand herds do not, on average, achieve the necessary targets. All measures of heat detection efficiency, although imprecise, show this is not a major problem with about 6% of heats missed. This has a negative effect on submission rates. Detection efficiency is an important issue for some individual herds as the consequences of poor heat detection are dramatic. The performance levels suggest that nutritional anoestrus and the effects of a spread calving pattern are the major causes of low submission rates. Conception rates of less than 60 % are reported. These are below those often suggested as typical for New Zealand herds. Much of the previous data has been taken from small study groups that may not adequately represent all herds. The common use of non-return rates may have created expectations that cannot be achieved in average herds as these are an optimistic measure of performance. Health events such as lameness are only reported for reference. Only limited health data is recorded although DairyMAN provides the flexibility to records such data. The variability in the type and degree of recording of these data is identified as a significant problem that limits the use of the available records. Some of the health events and especially lameness may have a large effect on the reproductive performance of many herds. Path models are developed in chapter 3 as an essential prerequisite to the development of the DairyFIX expert system. The models statistically confirm most of the relationships that have been previously considered important when evaluating herd reproductive performance. A number of factors including herd size and breed are shown to be associated with differing calving rates. The four week calving rate is shown to have strong indirect effects on submission rates, conception rates and herd in-calf rates. As such, it is one of the most important variables in seasonal herds. The importance of submission rates and conception rates is confirmed. Daily per cow milk production is shown to be a useful indicator of submission rates as both of these variables are directly influenced by nutrition. The models identify some limitations with using non-return rates as measures of conception. These generally give optimistic results that do not accurately reflect true performance. Such problems are compounded if reasonably accurate measures of heat detection cannot be obtained in herds with a very restricted mating period. Although the interactions between the performance and diagnostic indicators are largely understood from previous work this is the first time they have been brought together in statistically verified path models. The use of an on-farm information system (DairyMAN) was shown to be associated with improved herd performance including daily per cow milk yield and reproductive outcomes. DairyMAN user herds had cows of the same breed and genetic capacity. So DairyMAN users were able to produce more milk with animals of equivalent genetic merit, indicating that users achieved better management of the herd through improved attention to managerial details. This was associated with their adoption of DairyMAN, but not shown by this study to be a direct consequence of it. These findings are important because there is very little information confirming that on-farm information systems or central databases give true performance gains. This is despite the historical recognition of these systems and the rapid expansion in recent years. Justifying the use of more sophisticated tools such as an expert system would be more difficult if gains were not being achieved with the current technology. Calving induction was shown to be associated with some negative effects on milk yield and reproductive outcome. The New Zealand dairy industry does not currently favour the use of this management tool, but the impact any changes in management practices would have need to be evaluated with consideration of these effects. Calving induction is typically not used as recommended in New Zealand as many of the treatments are done too late to provide sufficient economic gains through increased lactation length and increasing the number of days from calving to the planned start of mating. Regional differences in performance were identified. DairyMAN user herds in the Manawatu had inferior conception rates while herds in the Taranaki had superior reproductive performance. These observed differences suggest a need to further identify causes of these differences, if performance is to be improved in some regions. The performance of individual cows and groups was examined in detail and statistical models developed for use in DairyFIX. Breed, lactation number, days calved at the start of mating and some health events were all shown to have an important impact on performance. The inferior performance of lactation 1 and 2 groups is having a large effect on performance. Cows in lactation 3 and 4 generally have the best performance with some reduction for aged cows. These aged cows do not dramatically affect overall herd performance because they are only a small proportion of most herds Jersey cows tended to show superior calving and submission rates. A number of complex models were developed for herds that pregnancy test and those that use non-return as the measure of conception. DairyFIX was developed to achieve two primary objectives. The first was to simplify the epidemiological approach to investigating herd reproductive problems. The system automates procedures that would otherwise be followed using DairyMAN and uses a graphical diagnostic interface to achieve this. DairyFIX quickly focuses on the important aspects of any performance deficit and reduces the time required to investigate a herd problem. Although DairyMAN is a comprehensive software package, users have difficulties due to its complexity and may invest a considerable amount of time exploring the program rather than focusing on the task required. The second objective of this project was to make expertise available for the user when examining herd performance. This required the use of the more sophisticated aspects of an expert system including the development of a "knowledge base" of information. DairyFIX consists of three sections. The first simply evaluates performance and determines if any problems exist. The second part considers the effect of the major components of performance such as the calving pattern and heat detection so that the primary causes of poor performance are identified. This section uses the statistical models previously developed to estimate expected performance. The third part of DairyFIX consists of several specific interrogation procedures for each area of poor performance. This section is not necessarily required for an operational system as the user can otherwise be referred to the appropriate reports in DairyMAN. Another module within DairyFIX was designed to assess the expected performance of a herd in subsequent seasons given a predicted herd profile. The models used for this purpose are similar to those that retrospectively evaluate performance. DairyFIX simplifies the investigative task and identifies the major causes of poor reproductive performance. It is anticipated that this tool will allow more dairy farmers and veterinarians to make effective use of DairyMAN while reducing the investment in time that is currently required.Item Use of genetic information about the herd in the design and management of dairy farm systems : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science majoring in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 2003) Bryant, Jeremy RalphThe aim of this thesis was to find ways of using the genetic information available about the cows to assist in improving the management of the herd and replacements. In particular models were developed which used Estimated Breeding Values to determine the feed demand of the cow and target liveweights for replacement heifers. The relationships between estimated breeding values (EBV) and cow performance at a range of feeding levels, and the effect of genetic merit on the partitioning of feed to milk or liveweight gain throughout the lactation, were also investigated. At low levels of feeding, the absolute differences in milk yield between cows corresponded to the absolute differences in breeding values between cows. However, at high levels of feeding the difference in milk yields between genetic groups are greater than the difference in breeding values. This constitutes a form of genotype x environment interaction, which has important practical and economic implications for daily farms, and for the expected value of genetic improvements. High genetic merit (HGM) cows partitioned a significantly higher proportion of metabolisable energy intake into milk than low genetic merit (LGM) cows in early (0.68 vs 0.62), peak (0.59 vs 0.57), mid (0.58 vs 0.56) and late lactation (0.53 vs 0.51) (HGM vs LGM respectively). In early lactation, HGM cows utilised more body reserves for milk production (-0.06 vs -0.004, for HGM and LGM, respectively). In addition, HGM and LGM cows appeared to compensate for low intakes in early lactation by reducing the level of MEI partitioned to milk, which probably prevented excessive weight losses. These results with grazing cows confirm published data with cows fed on other rations. Results from a grazing experiment, with 5 separate farmlets at 5 different stocking rates, were used to provide genetic information and performance per cow of a "calibration" herd corresponding to maximum profitability per farm (max EFS). The genetic and performance information for the calibration herd was then used to predict the performance of other cows or herds based on the difference in EBV for liveweight and milksolids. From these predicted values for liveweight and milksolids the "Genetic Feed Demand" (GFD) of the herd was calculated at max EFS. The GFD can then be used to adapt and improve the Comparative Stocking Rate (CSR) equation by replacing kg liveweight/ha with total GFD. Optimum values for the new CSR of 0.7 to 0.8 are proposed. This simple adjustment using genetic values provides a better estimate of the feed demand of the herd. From this an appropriate number of cows for the specified feed supply can be determined Another model was developed to use the liveweight EBV to formulate a set of liveweight targets for individual heifers of any breeds at different ages throughout the first two years of their life. Feeding regimes for the heifers were also proposed. A heifer herd management report was outlined that could be used by farmers and graziers to focus special attention on those individual heifers which were significantly lighter or heavier than their target weights for age. In conclusion, greater use should be made of genetic information of individual cows and herds when designing and managing dairy farm systems. Genetic values can be used in a number of ways to ensure cows or heifers are fed more appropriately so they achieve levels of performance, which are closer to their pre-determined genetic potential. Genetic information should also be included in tools that are used to model the management of dairy farm systems, as this will improve the accuracy of prediction.Item Effect of premating supplementation with monopropylene glycol on reproductive performance of dairy cows : a field trial : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Animal Science at Massey University, Turitea, Palmerston North, New Zealand(Massey University, 2005) Tuñon, Gonzalo EnriqueLow body condition score (BCS) at calving is associated with extended time to resume cycling in dairy cows. Prolonged postpartum anoestrous intervals (PPAI) are the major source of infertility in New Zealand dairy cows. Postpartum supplementation with monopropylene glycol (MPG), under controlled experimental conditions, was previously shown to reduce PPAI in heifers. This experiment tested this treatment in four large commercial dairy herds. During the 6-week period preceding the planned start of mating (PSM; Week 0), cows were drenched either once (MPGxl) or twice (MPGx2) daily with 200 ml MPG, or served as untreated controls (Con). A total of 2,122 cows were included in the analysis. Analyses were confined to the group of cows that were anoestrus at Week 6 or calved between Week - 6 and Week -4 relative to PSM (n = 684 to 714 per treatment). None of the four variables: oestrous behaviour during the treatment period, anoestrous rate one week before PSM, 3-week submission rate or 3-week pregnancy rate were affected by MPG. However, MPG did increase the 6-week and final pregnancy rates (P<0.005). with MPGxl having higher values (74.6% and 92.1%) than MPGx2 (69.1 and 88.5%) and Controls (67.7% and 88.1%), respectively. MPG-treated cows also produced more milk protein than the control-cows, by 0.01 and 0.017 kg of milk protein per day for MPGxl and MPGx2, respectively (P = 0.02), evidence of a metabolic effect of MPG. Recent studies suggest that diets that are optimal for follicle growth are not necessarily optimal for oocyte quality and subsequent embryo survival. It is hypothesised that MPGxl had positive effects on the follicle/oocyte through gonadotrophin-independent mechanisms and that MPGx2 had negative effects on the embryo. Probably the gonadotrophin-dependent effects necessary for ovulation could not be exerted in the present study because MPG was not administered for sufficient time to effect the LH surge. Both change in body condition score between Week - 6 and Week - 1, and proportion of cows that were anoestrus at Week -1, were influenced by herd, age and time of calving (P<0.05) but not by treatment (P>0.1). Treatment did not influence the proportion of anoestrous cows, treated with progesterone, which were inseminated after oestrus detection (n = 263). Change in BCS affected both milk yield and pregnancy rates, with cows that gained BCS producing less milk (P = 0.01) but showing higher 6-week pregnancy rates (P<0.05). This study highlighted that key factors influencing the percentage of anoestrus at PSM are cow age, time of calving and management of the herd.Item Reproductive efficiency in town supply dairy herds in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Science at Massey University(Massey University, 1978) Shrestha, Sundar LalThe objective of the study was to examine the reproductive performance of dairy cattle in Town Milk Dairy Herds in New Zealand. Breeding and production data for parous animals were collected from the records of twenty herds which ranged in size from 75 to 300 cows. Herd owners were members of the Wellington Hawke's Bay Livestock Improvement Association which provided herd testing and artificial breeding services. There were 12,056 calvings recorded involving 4,050 cows. Of these 9,898 were for Friesian, 672 Jersey, 1,066 Friesian Jersey cross cows and the remaining 420 other breeds and crosses. The parameters measured were calving interval, calving to first service interval, first service to conception interval, days open, inter-service interval, calving rate to first service and services per cow calving and were 383.7, 84.8, 11.3, 106.9, 43.7 days, 49.3% and 1.7 respectively for the pooled population. Data for calving interval and first service to conception interval were transformed for all analytical procedures - the unadjusted values for these parameters were 388.7 and 19.3 days respectively. The mean milk yield was 3,730 litres and the mean lactation length 291 days. Age, herd, season and year had highly significant effects on both productive and reproductive performance although the amount of variation that could be explained by these variables was small as far as reproduction was concerned. Any breed differences which may have been present were confounded with herd effects and no significant relationship was found between herd size and reproductive efficiency. This may have been due to an inadequate number of smaller herds in the sample. Significant negative correlations were found between average daily milk yield and calving, calving to first service and first service to conception intervals. Their values were so low as to be of little consequence. Reproductive efficiency increased up to the age of four years and then gradually declined whereas milk production increased up to the age of eight years before it declined. The youngest cows, particularly two year olds, which comprise a high proportion of the herd, performed poorly in nearly all reproductive parameters studied. The correlation between calving to first service and first service to conception intervals was -0.09 and the standard partial regression coefficients (β values) for calving to first service and first service to conception intervals on calving interval were 0.63 and 0.73 respectively. Thirty nine percent of the variation in calving interval was explained by days from calving to first service and 45% by days from first service to conception. A high incidence of short (11.6%) and long (49.5%) returns, together with an average inter-service interval of 44 days, indicated that detection errors and heat detection efficiency were important problems contributing to delays in breeding and increased numbers of services per cow calving. Conscious management decisions to with-hold cows from breeding to meet specific seasonal needs may have compounded this problem. Significant seasonal effects were observed with superior results during the spring irrespective of whether cows calved or were being bred at that time. Year differences in both productive and reproductive performance were also noted with best results occurring during years which recorded climatic conditions as being most suitable for pasture growth. The number of abortions recorded during the course of the investigation were few. Where aborting cows were retained their breeding performance during the year following abortion was poor but this effect did not appear to carry-over to their performance in subsequent years.Item Monitoring liveweight to optimise health and productivity in pasture[-]fed dairy herds : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University(Massey University, 2011) Alawneh, IbrahimTechnological advances now make it possible to continuously record and monitor a range of outcomes on dairy farms including individual cow milk yields, environmental temperature and rainfall. These facilities enhance the ability of herd managers to recognise deviations from what is accepted as normal, prompting timely corrective intervention. The objective of this thesis is to demonstrate how liveweights recorded using walkover weighing (WoW) technology can provide information that can be used to better-manage a range of activities on dairy farms, particularly reproduction and herd health. Analysis of daily WoW recorded over the first 100 days of lactation have shown that the standard deviation of daily LW measurements across parities was 17 kg on average. A near perfect association between liveweights measured statically and WoWs (concordance correlation coefficient 0.99, 95% CI 0.99 to 1.0) was observed. After controlling for the effect of liveweight at calving and long term liveweight change using a mixed-effects linear regression model, the autocorrelation between WoWs recorded on successive days was 0.21, decaying to zero by eight days. This study showed that by using a standalone automatic WoW system positioned in the exit race of a rotary milking parlour, it was possible to record LWs of individual cows on a daily basis and, with controlled cow flow over the weighing platform (allowing for sufficient succession distance to prevent congestion), results were similar to those recorded using conventional, static weighing techniques. Two observational studies were conducted to investigate the relationships between LW, LWchange ( LW) and clinical lameness. In the first study, LW loss in the first 50 days in milk increased the risk of a lameness event being diagnosed after 50 days in milk by a factor of 1.80 (95% CI 1.00 to 3.17). The risk of lameness was greatest for high yielding cows that lost excessive LW (risk ratio 4.36, 95% CI 4.21 to 8.19). The second study quantified LW immediately before and after the diagnosis of lameness events. For lame cows, liveweight decreased up to three weeks before the date of diagnosis and for up to four weeks after. The total liveweight loss arising from a single lameness episode was, on average, 61 kg (95% CI 47 to 74 kg). The results of this study show how liveweight records for individual animals can be used to enhance a herd manager’s ability to detect lame cows and present them for treatment. Prompt detection and treatment of lame cows presents an opportunity to shorten recovery times, with positive follow-on effects in terms of animal welfare. LW was assessed as a means for enahancing the sensitivity and specificity of oestrus detection. The sensitivity and specificity of detecting true oestrus events using LW combined with tail paint and visual observation was 0.86 and 0.94, respectively. The effect of LW in the first four weeks after calving ( LWlong) and LW change around the time of the Planned Start of Mating ( LWshort) on the time taken for cows to conceive relative to the Planned Start of Mating was quantified. Planned Start of Mating to conception intervals were influenced by LW change during both of these periods, though LWshort had a greater effect compared with LWlong. The findings of this study better define the impact of long- and short-term liveweight change on reproductive performance, providing the opportunity to design feeding programmes in pasture fed dairy herds that have positive effects on fertility. The studies presented in this thesis contribute knowledge to the role of LWmonitoring as a tool to better-manage seasonally calving, pasture fed dairy herds. While ‘traditional’ usage of walkover scales on dairy farms has involved the recording of LWand LWchange as a means for monitoring and adapting changes to the herd feeding program, the studies presented here have shown how LW records have the potential to provide information that can be used to better manage a range of herd level activities, particularly those related to reproductive management and health.Item Phenotypic relationships between milk protein percentage, reproductive performance and body condition score in Irish dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Sciences (MSc) at Massey University, Palmerston North, New Zealand(Massey University, 2009) Yang, LinnaA positive phenotypic correlation between milk protein percentage and reproductive performance in dairy cattle, especially during early lactation has been recently reported. The objective of this study was to quantify the relationship between milk protein percentage and different measures of fertility in Irish, seasonal calving, dairy cattle using data from experiments comparing strains of Holstein-Friesian cows under different feeding systems. The relationships between body condition score, milk production and fertility were also investigated. The data used in this study consisted of 584 lactation records over a 5-yr period. Principal component analysis and logistic regression was used to study the relationship between milk protein percentage and fertility performance of the cow. Greater milk protein percentage during the first 60 days post-calving was associated with better reproductive performance. The probability of a cow being submitted in the first 21 days of the breeding season increased with increased milk protein percentage during early lactation. Similarly, the probability of a cow becoming pregnant to its first service or to the whole breeding season also increased. Cows were classified as either high or low milk protein percentage based on their protein percentage over the whole lactation. Cows in the high milk protein group had a 7% greater conception rate compared to cows in the low protein percentage group. In conclusion, cows with higher protein percentage, especially during early lactation are submitted earlier in the breeding season, and have a higher conception rate. Physiologically, the shortage of glucose caused by negative energy balance restricts the synthesis of milk protein in the udder. On the other side, negative energy balance also causes the reduction of IGF-I, LH and oestradiol, which consequently delay the ovarian follicular development and finally reduces fertility. Therefore, there is a biological explanation for the association between milk protein percentage and fertility performance.