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Item The gross composition, fatty acid composition, and processability of milk from cows milked once and twice a day under New Zealand grazing conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Palmerston North, New Zealand(Massey University, 2023) Sanjayaranj, InthujaaIn New Zealand, milking once a day (OAD) is practised by some farmers, with the majority of farmers milking twice a day (TAD). Once-a-day milking provides several benefits such as reduced labour cost, improved labour efficiency, improved health and reproductive performance of cows, and additional employment opportunities for farmers. Once-a-day milking causes a reduction in milk yield and modifies milk composition by increasing the fat and protein percentages. The main aim of this thesis was to study the effect of OAD milking on the gross composition, fatty acids composition, and processability of milk. To achieve this, the milk from 232 cows from a OAD herd and 182 cows from a TAD herd were collected in a full season in early, mid-, and late lactation. The samples were analysed for milk composition and fatty acid composition using Fourier-transform mid-infrared (FT-MIR) spectroscopy. Calibration equations for individual and grouped fatty acids were developed using FT-MIR calibrator software. Milk coagulation properties (rennet coagulation time, curd firming rate, and curd firmness) were analysed using a Formagraph. In addition, a SNP (rs109421300) in the diacylglycerol acyltransferase 1 (DGAT1) region on bovine chromosome 14, which is associated with a higher fat percentage in milk, was selected to study its association with fatty acid composition. Solid fat content at 10°C (SFC₁₀), a parameter that predicts butter hardness, was calculated using an equation developed from the proportions of fatty acids. The proportions of de novo synthesised fatty acids (C8:0-C14:0) were significantly higher, and the proportions of preformed, long-chain fatty acids (mainly C16:0 and C18:0) were lower in milk from cows milked OAD compared with cows milked TAD. Milk coagulation properties were superior for Jersey cows compared with Holstein-Friesian and Holstein-Friesian × Jersey cows milked OAD and TAD. The CC genotype of SNP rs109421300 was associated with higher fat yield, fat percentage, protein percentage, and SFC₁₀. Milk from OAD cows had lower proportions of C16:0 suggesting it would produce more easily spreadable butter. Selecting cows with the CC genotype would be suitable for the New Zealand dairy industry with the current payment system, however, the CC genotype was less suitable for making more easily spreadable butter. Overall, there were some significant differences noted between milk from cows milked OAD and TAD in terms of fatty acid composition and processability.Item The prevalence and production effects of liver fluke (Fasciola hepatica) in New Zealand cattle including evaluation of diagnostic tests : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand(Massey University, 2023) Dowling, AndrewThe liver fluke Fasciola hepatica, infects cattle worldwide and is considered a parasite of regional importance in New Zealand although the impact on milk production in that country have not been studied. The test characteristics of two antibody detection ELISAs; IDEXX ELISA (IDEXX Fasciolosis Verification) and an In-House assay using unrefined excretory secretory antigens, plus a coproantigen ELISA (Bio K 201–Monoscreen AgELISA) and faecal egg counts (FEC) were assessed against the gold standard of total fluke counts in naturally infected cattle (cows=29, steers=10). Vat milk of dairy herds on the West Coast of the South Island was assessed for liver fluke infection using the IDEXX ELISA in the autumn, near the end of one lactation (n=430), and spring, near the beginning of the subsequent lactation(n=403). A total of 156 questionnaires determining awareness of liver fluke infection and drenching practices were completed. A cross sectional study of 11 herds (n=1314 cows) in autumn and a longitudinal study of 4 herds (n=485 cows) in spring and autumn used the IDEXX ELISA (measured as SP%) on serum to analyse associations between liver fluke infection and milk production parameters in individual cows. A subset of cows was also faecal sampled for coproantigen and FEC analysis. Notably, a negative linear effect of the loge(total fluke count+1) on liveweight (p=0.02) was found and the coproantigen values showed a significant (p=0.01) quadratic effect for loge(total fluke count+1). The survey showed that infection of herds at a level likely to cause production losses on the West Coast is common, with regional clustering. Milk Fat % decreased 0.0004% points for every 1SP% increase (p=0.004), being 0.05 %points lower for cows with SP%150 than cows with SP%30, and 0.22 %points (p=0.014) lower in cows where SP% increased from ≤30 to ≥150 during lactation compared that those remained ≤30 with an economic cost of $55.19 per infected cow. Of the tests compared, the IDEXX ELISA was superior to the In-House ELISA for sensitivity (Se) and specificity (Sp) but the coproantigen ELISA had the highest Se (96%) and Sp (96%). Overall, liver fluke infection was common in dairy cows but the infection intensity was low, nevertheless a small effect on MF% was determined.Item Genetic parameters of fertility traits of cows milked once daily versus twice daily in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Manawatū, New Zealand(Massey University, 2023) Jayawardana, Jayawardana Mudiyanselage Dinesha RajineeIn New Zealand about 55% of dairy herds are milked twice daily (TAD) and about 9% of herds are milked once daily (OAD) for their entire lactation, with the balance of herds using variable milking frequencies across the lactation. The general aim of this thesis was to estimate genetic parameters for fertility traits of spring-calved OAD and TAD milking cows in New Zealand. Cows milked OAD for the entire lactation were more fertile than cows milked TAD for the entire lactation. Heritability and repeatability estimates for milk production and fertility traits were broadly consistent for cows that were milked either OAD or TAD for their entire lactation. Though genetic correlations between milk production and fertility were antagonistic in both milking systems, correlations between milk production and the key reproductive metrics of 6 wk in-calf, not in-calf rate and 6 wk calving were less strong in cows milked OAD compared with TAD. In both OAD and TAD milking populations, individual breed effects for milk, fat, protein and lactose yields were in favor of Friesian (F) cows; however, maternal breed effects for yields were in favor of Jersey (J) dams. Jersey cows were more fertile than the F cows in both milking populations, but maternal breed effects for fertility traits were in favour of F dams. Favourable F×J heterosis for milk production and fertility traits were significant in both milking cow populations. Recombination loss effects were sometimes favorable for production and fertility traits, but most estimates were small with larger standard errors. A genome-wide association study (GWAS) was conducted using 1,537 spring-calved dairy cows genotyped with Bovine Illumina 50K single nucleotide polymorphisms (SNPs) chips in two Massey University dairy herds. Four SNPs on chromosome 14 were highly significant for fat and protein percentages and associated genes were DGAT1, SLC52A2, CPSF1 and MROH1. The GWAS identified 10 candidate genes (KCNH5, HS6ST3, GLS, ENSBTAG00000051479, STAT1, STAT4, GPD2, SH3PXD2A, EVA1C and ARMH3) associated with fertility traits, which relate to functions, reduced metabolic stress and increased insulin secretion during the mating period, early embryonic development, fetal growth, and maternal lipid metabolism during the pregnancy period. Overall, the results of this thesis indicate milking OAD for the entire lactation improves the fertility performance of dairy cows but reduces milk production. The antagonistic genetic correlations between milk yield and key fertility measures were weaker in the OAD milking population than in the TAD milking population. The findings of this thesis can be used to develop a selection index for production and fertility traits in OAD milking cow population in New Zealand.Item Impact of plantain (Plantago lanceolata) based pasture on milk production of dairy cows and nitrate leaching from pastoral systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Manawatu, New Zealand(Massey University, 2023) Nguyen, Truong ThiIn temperate dairy systems, the traditional perennial ryegrass (Lolium perenne)-white clover (Trifolium repens) (RGWC) pasture often has excessive nitrogen (N) content relative to the N requirement of animals, posing a risk of nitrate (NO₃⁻) leaching into the environment. Recently, incorporating plantain (Plantago lanceolata) with RGWC pasture has been increasingly used to improve economic and environmental benefits for dairy farms. However, the impact of plantain incorporation on farm productivity and NO₃⁻ leaching at the farm level has not been fully understood. The objectives of this thesis were to quantify the effect of incorporating increasing rates of plantain in grazing swards on pasture production, milk yield and composition of dairy cows, and NO₃⁻ leaching from pastoral dairy systems. To address the objectives of the thesis, a grazing trial was implemented at a research dairy farm between September 2019 and December 2021. Pasture treatments were RGWC (perennial ryegrass cv. ONE⁵⁰ and white clover cv. Tribute), RGWC + low plantain (cv. Agritonic) rate (PLL), RGWC + medium plantain rate (PLM), and RGWC + high plantain rate (PLH). Pastures were established with 20 experimental plots and four adaptation areas in April 2019 and were rotationally grazed by dairy cows over 22 grazing events during the experimental period. In each grazing, 60 or 80 cows were assigned to graze for 6 days in their adaptation areas and 1.5–3 days in the experimental plots. The experimental cows were managed under a typical practice, milking twice daily, offering grazing pasture and approximately 25% supplementary dietary feeds. Measurements were conducted to quantify the yield, botanical composition and nutritive value of the pasture, milk yield, milk composition and N excretion of dairy cows, and NO₃⁻ leaching from the pastoral system. The results showed that, over the first two lactation years after sowing, plantain-based pastures have a similar dry matter yield and contain higher water content, non-structural carbohydrates, minerals, and bioactive compounds than the RGWC pasture. The average plantain proportion in the swards over the first two years after sowing was 32% in PLL, 44% in PLM, and 48% in PLH, which increased in the first 15 months and declined to 20% in PLL and 30% in PLM and PLH at day 705 after sowing. Cows grazing the plantain-based pastures had a similar milk yield, composition and yield of solids, protein, fat, and lactose as those grazing the RGWC pasture. Furthermore, when 25% plantain was included in the diet of cows in late lactation, it resulted in a 44% increase in urine volume and a 29% reduction in urine N concentration by 29%. By incorporating an average of 30% and 50% plantain with RGWC pasture, NO₃⁻ leaching was reduced by 32 and 52%, respectively, over two drainage years after establishment, with a greater reduction in the first year than in the second year. Among sowing rates, PLM resulted in the greatest decrease in NO₃⁻ leaching, with 64% in the first year and 41% in the second year. The decreased NO₃⁻ leaching was associated with increased plantain content, enhanced herbage N uptake, reduced UN excretion of dairy cows and a lower N load in urine patches. In conclusion, in a typical practice, as in the present study, incorporating 30–50% plantain with RGWC pasture decreases NO₃⁻ leaching from pastoral systems without adversely impacting farm productivity for at least two years from sowing. However, the reduction of plantain content in the second year suggests further measurements to determine the effectiveness of plantain-based pasture in the longer term. In the conditions and time scale of the present study, the medium plantain rate treatment (PLM) is suggested to achieve a high effectiveness of plantain incorporation in reducing NO₃⁻ leaching.Item The effects of the application of large amounts of nitrogen fertilizer on milk yield, reproductive performance, and energy balance of spring-calved high genetic merit cows : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Sciences in Animal Production at Massey University, Palmerston North, New Zealand(Massey University, 2005) Ordóñez, AlfredoThe intake of crude protein (CP) in amounts considerably above the cow's requirements has been associated by several overseas (OS) reports with reduced cow performance. In New Zealand (NZ), the CP content of pasture during spring is usually above the cow's requirements. During this time, application of nitrogen (N) fertilizer is a common practice which further increases the CP content of pasture. Despite this fact, few experiments have studied the effect of high CP intake on cow performance in NZ, and the existing results are not conclusive. Therefore, the objective of this experiment was to measure the effect of two levels of CP concentration in pasture caused by application of different amounts of N fertilizer, on milk yield, reproductive performance, and energy balance of grazing, spring-calved, high genetic merit cows in NZ. Two groups, each of 20 high genetic merit cows, were offered a common pasture allowance (46 kg OM/cow/day) over the first 101 days postcalving, but from pasture which contained either a lower (low CP group) or a higher concentration (high CP group) of crude protein. The difference in CP concentration was created by applying either no N fertilizer or 35 kg of N fertilizer after every grazing. Herbage masses were measured on every paddock weekly, and every day pregrazing and postgrazing, using a rising plate meter. These values were used to calculate pasture growth, and apparent dry matter intake per group. Pasture composition was measured by near infrared spectroscopy. For each cow, milk yield and composition was measured by weekly herd tests. Reproductive performance was assessed by scanning of follicles and corpora luteal from day one until day 40 postcalving, and from 10 days before the predicted artificial insemination (Al) until 35 days post Al. Progesterone concentrations were measured in milk samples taken every second day. Liveweight and condition score of each cow were measured weekly, and concentrations of NEFA and IGF1 were measured in blood samples taken II once every week. Energy balance was calculated as theoretical energy requirements minus estimated energy intake, and feed conversion efficiency was also calculated. When compared with the low CP paddocks, the high CP paddocks produced more pasture (+1,260 kg OM/ha in 101 days) and it was of higher quality (11.8 vs. 11.4 MJ ME/kg OM; 83.4% vs. 81.2% digestibility; 24.5 vs. 21.6% CP). The apparent daily intakes of OM and ME of the two groups were not significantly different (16.2 and 15.9 kg OM/cow; 195 and 184 MJ ME/ cow). However, the high CP group ate significantly more CP than the low CP group (4.2 vs. 3.5 kg CP/cow/day, and had a higher blood urea concentration (7.8 vs. 5.3 mmol/I). There were no significant or consistent differences between the two groups in milksolids yield (1.84 vs. 1.91 kg MS/cow/day for the high and low CP groups), reproductive measurements, liveweight, condition score or IGF1 concentrations. However, the high CP group had significantly lower NEFA concentrations than the low CP group (0.45 vs. 0.56 mmol/I). The high CP group had lower apparent feed conversion efficiency than the low CP group, which may have been partially due to the calculated value of 3.2 MJ ME extra required per day to excrete the extra urea from the high CP group. In conclusion, even though the high CP group had higher blood urea concentrations, no significant differences in cow performance were detected between the two groups. The application of 130 kg N/ha produced an extra 1,264 kg OM/ha, which would have been expected to produce an extra 140 kg MS/ha, although this increase in MS yield may have been reduced slightly (by 9%) by the lower calculated feed conversion efficiency of the high CP group. Subject for further research include attempts to increase the feed conversion efficiency of animals grazing pastures with high CP content, through the use of sources of extra rumen degradable energy; the effect of diets high in CP on embryo quality and viability; and the ecological impact of using large amounts of N fertilizers.Item Effects of nutrition on milk production and reproduction of dairy cows : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatū, New Zealand(Massey University, 2022) Yapa Hetti Pathirennehelage, Sagara Nelum KumaraSri Lanka is developing its dairy industry in a concerted effort to become self-sufficient in dairy products. Dairy farming in Sri Lanka occurs largely in small (≤10 cows) or medium (11-100 cows) scale farms, characteristically using diets that are based on tropical forages and various concentrate supplements. Despite this reliance on forages, little is known about their nutritive value or about the most appropriate ways of managing such forages in dairy rations. Consequently, per cow yields are generally low, and poor fertility is a significant limitation to the viability of the dairy industry. The primary objective of this thesis was to examine the management of forages in Sri Lankan dairying systems and the consequences of that management upon dairy cow productivity and fertility. As there was a lack of systematic information regarding the nutritive value of forage-based diets, generating such data was the first focus of the study. These data were used to calculate the extent to which supplied diets met the energy and protein requirements of dairy cows. Direct observation of cows and blood-based measures of metabolic status were used to verify cows’ nutritional status. As there was also a lack of systematic information on the fertility of Sri Lankan dairy herds, this was also evaluated. The first study (Chapter 3) investigated the feeds and rations used in medium-scale dairy production systems of Sri Lanka. Metabolisable energy (ME) and crude protein (CP) content were assessed in the two most commonly used forages (Guinea grass ecotype A (Panicum maximum), hereafter referred to as Guinea grass, and Hybrid Napier CO-3 (Pennisetum purpureum* P. americanum), hereafter referred as CO-3 grass) and in the secondary forages Gliricidia (Gliricidia sepium) and maize stover (Zea mays L.). Mean ME and CP content of Guinea and CO-3 grasses were 7.8 and 9.3 MJ/kg dry matter (DM) and 8.0 and 8.8% DM, respectively. Total dietary intakes of ME and CP were calculated using these values. Daily ME intake across the entire late-dry to mid-lactation period was consistently 7% lower than calculated requirements, whilst CP intake (13.5% DM) was below requirements in early lactating (16 18% DM required) but not dry cows (10 12% DM required). Metabolic profiling (serum albumin, urea, β hydroxybutyrate and non-esterified fatty acid concentrations) over the same period confirmed the presence of widespread energy and protein deficiencies (Chapter 4). However, body condition scores (BCS) were consistent over the lactation at 4.3 4.5 (1-10 scale). Insulin-like growth factor-1 (IGF-1) concentrations (Chapter 6) were higher during Days 1-14 of lactation than during Days 43 57 (60.8 ± 2.6 ng/mL vs. 72.3 ± 3.6 ng/mL), and also in cows with higher post-calving BCS, but were not clearly related to calculated energy status. The major conclusion from Chapters 3 and 4 was that nutritional deficiencies in Sri Lankan dairy cows could largely be attributed to poor control of stage of maturity of harvested forages. Reproductive performance of cows (Chapter 5) was assessed using farm records (including farmers’ observations of oestrus) and serum progesterone assays over Days 43-120. Progesterone profiles showed that 61.6% of cows resumed ovarian cycles by Day 120; but only 42% of these were observed in oestrus. Further, of the cows that progesterone assay had not shown resumed cyclicity by Day 120, 20.9% had been considered by farmers to have displayed oestrus. Pregnancy rates were 12.7% by Day 120 and 59% by Day 400, average intervals from calving to conception were 196.1 ± 8.9 days, and from calving to first artificial insemination (AI) were 116.0 ± 2.5 days, with 3.05 ± 0.2 inseminations required per conception. The high proportion of anoestrous cows and low conception rates were largely attributed to inadequate nutrition during the transition and early lactation periods, compounded by inaccurate oestrus detection. Parity (1st) and breed (Holstein-Friesian, HF) of cows were both risk factors for delayed resumption of oestrous cycles. Concentrations of IGF-1 were largely unrelated to reproductive outcomes, except those values on Days 43-57 were negatively related to the interval between calving and first AI. Chapter 7 investigated the nutritional composition of ryegrass-white clover pastures in New Zealand that were grazed with different rotation lengths, on the hypothesis that longer rotations lengths would result in more mature swards, with lower quality herbage. Farms were selected with longer (winter ~35 days, spring ~25-30 days) or shorter (winter ~30 days, spring ~20-25 days) grazing rotations. Both ME and CP were reduced by higher pre-grazing DM and rotation length, whilst post-grazing DM and residual height were positively correlated (r2 ≥0.8) with pre-grazing DM. Thus, the quality of the forage from long grazing rotations was poorer, and, therefore, the amount of DM consumed by grazing cows may be affected. Many cow-related factors significantly affected the reproductive performance (Chapter 8) of dairy cows in New Zealand. Cows with >85% of HF genes had lower pregnancy rates in the first three (PR21) and six (PR42) weeks from the start of breeding compared with those with ≤85% HF genes. Cows of parity 1-4 had higher PR21 and/or PR42 than those of parity ≥5. Pregnancy rate to first service (PREG1) was lower (odds ratio (OR): 0.7) in cows with higher BCS change ( 0.5 to 1 units: 1 10 scale) between calving and the BCS nadir. Cows that calved in July had higher PR21, and PR42 (OR:1.96, and 2.51, respectively) than those that calved in September, while cows that calved in August had higher submission rates in the first three (SR21) and six (SR42) weeks from the start of breeding (OR: 2.39, 3.21, respectively) than those that calved in September. Higher fat production and total milk solids production were associated with significant negative energy balance (NEB) (≥ 30 MJME/day), but NEB was less (or was positive) in cows with lower milk yields. Therefore, it appears that breed, BCS, parity, energy balance, calving month and milk composition are all useful indicators of future reproductive efficiency. Taken together, these studies for the first time, characterise the quality of dairy forages in Sri Lanka and the adverse effects of inadequate nutrition upon cow productivity. The studies in New Zealand confirmed that forage quality and intake were adversely affected by over-maturity of pasture, driven primarily by rotation length, and these findings supported conclusions made regarding forages in Sri Lanka. Characterisation of reproductive performance of Sri Lanka dairy cows showed that it was at a level that undermines the viability and productivity of the dairy industry. Reproductive performance is not only impaired because of the adverse effects of nutrition, but also due to the inadequacy of farmers’ reproductive management. Whilst these results are ostensibly depressing, they point to some relatively easy-to-implement interventions (e.g. improving forage management, better ration formulation, better education of farmers) to boost the future of the Sri Lankan dairy industry.Item A study of milk production as it affects lamb growth in Romney and Cheviot crossbred sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science of the University of New Zealand(Massey University, 1952) Roberts, Euan MauriceRomney and Cheviot Threequarter bred 6 year old ewes, all with twin lambs, were found to produce similar quantities of milk in a 12 week lactation. The Cheviot halfbred ewes produced less milk than either the Romney or 3/4 Cheviot ewes but the disadvantage was not thought to be of an hereitary nature. Both Cheviot groups of ewes gave significantly richer milk than the Romney group. When mated to Southdown rams the ewes of the Romney and each Cheviot breed produced lambs which made similar liveweight gains.Item A study of the Romney fat lamb ewe, with particular reference to milk secretion and its effect on fat lamb production : thesis submitted by "392" [Alan Graham Logan] for the M. Agr. Sc. degree at Massey University(Massey University, 1946) Logan, Alan GrahamOne of the distinguishing characteristics of mammals, is the dependance of the young, during early post-natal life, on nourishment secreted by the mammary gland of the mother. Hence milk secretion is of fundamental importance in all our farm animals with the exception of poultry. The essential attributes of milk (viz., high water content and liquid state, high digestibility, high protein content of excellent biological value, high calcium and phosphorus and the presence of most of the necessary vitamins) are specially suited to the needs of young rapidly growing animals. In dairy cattle extensive study has been made of milk producing ability and conscious effort made to improve this by breeding, and nutrition. Comparison of the characteristics of modern dairy cattle (highly developed milking qualities but inferior meat carcasses) and of beef cattle (early-maturing and good carcass quality but often poor milk yield) clearly indicate the extent of improvement from the wild form and the variation in productive efficiency of different types. Valuable work on the milk-producing ability of other species, and its relationship to the welfare of the young has been carried out by Bonsma and Oosthuizen (1) and Donald (7) with Sows; and Ritzman (30), Fuller and Kleinhanz (10), Neidig and Iddings (24), Bonsma (2,3), 30a, Pierce (27,28) with ewes of non-milking breeds, and by several workers with specialised milking sheep, Scheingraber (31), Muhlberg (23), Maule (17). [From Introduction]Item Genetic and genomic studies on milk production and composition, and longevity in New Zealand dairy goats : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Manawatu, New Zealand(Massey University, 2020) Scholtens, MeganThe New Zealand dairy goat industry is important for producing and exporting high-quality specialised dairy products aimed at niche markets. Efforts to increase the quantity and composition of goat milk will improve profits for farmers and deliver significant economic benefits to New Zealand. However, no formal program exists for the genetic improvement of dairy goats. Therefore, the general aim of this thesis was to perform genetic and genomic studies that contribute to the design of the breeding program for New Zealand dairy goats. The first studies estimated variance components and genetic parameters of total lactation yields of milk, fat and protein, somatic cell score and longevity. The main findings suggest sufficient variation and favourable genetic correlations between these traits, supporting their inclusion into a selection index that predicts profit per animal. A random regression test-day model was then used to predict lactation curves of milk, fat, protein and somatic cell score. Using this model for genetic evaluation will enable the dairy goat industry to move from total yields into the prediction of lactation curves, enabling more accurate predictions and the opportunity of selecting for extended lactations. The first genome-wide association study of dairy goats in New Zealand was conducted using 3,732 animals genotyped with the Caprine 50K SNP chip. A highly significant region on chromosome 19 was associated with yields of milk, fat and protein, and somatic cell score, and a region on chromosome 29 was associated with somatic cell score. A prototype single-step BayesC model was developed to predict genomic breeding values and demonstrated that including genomic information into the evaluation can increase the accuracy of predictions compared to the traditional methods based on pedigrees alone, which is currently implemented in the New Zealand dairy goat industry. This thesis demonstrates that a single-step prediction model that uses genomic information would put the New Zealand dairy goat industry in a very good position to implement a genomic selection scheme. Further studies are required to define clearer breeding objectives and to systematically design a breeding program for the genetic improvement of New Zealand dairy goats.Item Live weight and growth of dairy heifers are important for subsequent milk production and reproductive performance : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Turitea, Palmerston North, New Zealand(Massey University, 2019) Handcock, Rhiannon ClareIn the pasture-based farming systems that occur in New Zealand, dairy heifers tend to follow a seasonal pattern of growth in response to pasture quality and availability. The industry recommended liveweight-for-age targets for dairy heifers are 30% of mature liveweight (LWT) at 6 months of age, 60% at 15 months of age and 90% at first calving. Target growth rates are calculated by linear interpolation, thereby creating a mostly linear planned trajectory of growth from three to 22 months of age. The general aim of this thesis was to investigate the effects of LWT and growth on dairy heifer performance in the New Zealand pasture-based system. In this thesis, LWT records from 189,936 spring-born dairy heifers were provided by Livestock Improvement Corporation to model growth curves from three to 22 months of age. Holstein-Friesian (F) heifers were heavier than Jersey (J) heifers from three to 22 months of age, and FxJ crossbred heifers were heavier than the mean of the purebreds due to positive heterosis effects. Additional data of calving dates and milk production records were provided by Livestock Improvement Corporation. Live weight between three and 21 months of age had significant impacts on milk production and reproductive performance. As LWT of heifers increased, milk production and probability of calving and calving early increased up to a maximum. Further increases in LWT past the maximum point did not result in increases in milk production, and for reproduction (stayability and calving rate) resulted in a decline in probability. For heifers that were below average in LWT, significant improvements to milk production and reproductive performance would be expected by increasing LWT. For example, the mean LWT of 15-month-old Holstein-Friesian-Jersey crossbred (FJ) heifers was 301.5 kg. These “average” heifers were estimated to produce 436 and 1,477 kg more energycorrected milk (ECM) than “below average” 250 kg heifers in first-lactation and threeparity accumulated yields, respectively. Additionally, stayability to first, second and third calvings were superior for “average” heifers (93.6 vs 89.3% for first, 78.2 vs 70.6% for second and 64.7 vs 57.5% for third) and first calving 21-day calving rate (C21_2yo; 81.9 vs 78.0%) compared with “below average” heifers. For heifers that were above average in LWT, significant improvements to milk production would be expected by increasing LWT, however, at the heaviest LWTs a reduction in reproductive performance would be expected. For example, FJ heifers that were 375 kg at 15 months of age were estimated to produce 554 and 1,434 kg more ECM than “average” 300 kg heifers in first-lactation and three-parity accumulated yields, respectively. However, stayability and C21_2yo were similar for 375 kg (93.4%, 78.9%, 63.8% and 79.8% for stayability to first, second, third calving and C21_2yo, respectively) and 300 kg FJ heifers. Heifers that were at the heaviest LWTs, for example, 425 kg at 15 months of age were estimated to have the greatest ECM yields, but had a lower stayability and C21_2yo compared with “average” heifers (88.4%, 72.5%, 55.3% and 76.8% for stayability to first, second, third calving and C21_2yo, respectively). The greatest benefits to both reproduction and milk production would be expected by increasing LWT of the lightest heifers at each age studied. In a prospective study, milk production did not differ between heifers that grew in a seasonal manner (slow then fast) compared with the target growth trajectory (linear) between six and 15 months of age. There was a difference in the age at which puberty was attained, such that heifers that grew to the target growth trajectory were younger at puberty compared with those grown in a seasonal manner, however, there was no difference between treatments in the date of first calving or first lactation milk production. These results indicate that there were limited disadvantages to growing heifers slower over their first winter, provided they caught up to target LWT by first mating. Overall the results of this thesis indicate that having heifers heavier through the precalving rearing phase (three to 21 months of age) has the potential to improve reproductive success and milk production, with the greatest advantage seen by increasing LWT of the lightest heifers. This information can be used to develop guidelines which may improve productivity and survival of dairy cattle in New Zealand.