Browsing by Author "Hickson, Rebecca"

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The effect of birth rank and age of dam on the reproductive performance of ewe replacements managed under New Zealand pastoral conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
(Massey University, 2020) Pettigrew, Emma
Selecting replacement ewes that are born to ewe lambs is an uncommon practice in New Zealand; however, there is the opportunity to increase ewe efficiency and increase the rate of genetic gain if the practice is adopted. Lambs born to ewe lambs may be lighter until up to four years of age, compared with lambs born to mature ewes, however there are few unbiased comparisons of performance. The objective of this study was to compare the reproductive performance of replacements born to either mature ewes or ewe lambs. A study with 115 singletons or twins born to mature ewes or ewe lambs, found that singletons born to mature ewes were heaviest, twins born to mature ewes and singletons born to ewe lambs were intermediate, and twins born to ewe lambs were lightest for their lifetime to eight years of age. There was no difference in lifetime lamb production among these four groups, and there was no difference in the efficiency among the ewe groups, however the power of that study may have been limited by relatively low numbers of animals. A second study utilised 1082 mature ewes and 1026 ewe lambs, bred to the same rams at the same time, producing 2701 lambs, of which, 358 lambs were selected as replacements. Lambs born to ewe lambs were lighter than lambs of the same birth rank born to mature ewes from birth until weaning and had lower rates of survival at tagging and from tagging to weaning. The relationship between the probability of survival to weaning and birth weight was quadratic, and differed for each birth-rank-by-age-of-dam cohort. Lambs born to ewe lambs, and as triplets to mature ewes have lower rates of lamb survival and growth to weaning, so farmers need to prioritise time and resources to improve these. In the third study investigating reproductive performance of replacements born to either ewe lambs or mature ewes, 135 twins born to mature ewes, 135 singletons born to ewe lambs, and 88 twins born to ewe lambs were bred (if heavier than 39 kg at breeding) as ewe lambs. Of the ewe lambs that were heavy enough to be bred, there was no difference in the number or weight of lambs produced at weaning from the three groups, but twins born to ewe lambs were less likely to reach breeding weight targets. During their second breeding (at approximately 18 months), all ewes were bred, and there were no differences in the number or weight of lambs produced at weaning. This indicates that the offspring of ewe lambs could be selected as replacements, but that farmers need to consider selecting based on weight at weaning if they intend to breed the ewe lambs at eight months of age. Further work, including an economic analysis, and continued investigation into the lifetime production and efficiency of ewes born to ewe lambs is needed. Genomic technologies are currently being used by scientists to increase the accuracy of selection of replacement animals for traits that are difficult to measure in the adolescent at the time of selection. Reproductive performance as a ewe lamb has an impact on the lifetime production of a ewe, and live weight at the time of breeding can heavily influence the likelihood of the ewe lamb becoming pregnant during her first breeding. Using ewe lambs from the second and third studies, and additional ewe lambs, five gene regions were found to be associated with live weight at eight months of age in ewe lambs, and two gene regions were found to be associated with the occurrence of pregnancy during their first breeding at eight months of age. Further investigation into these, and other, gene regions associated with reproductive traits in ewe lambs could allow the use of marker assisted selection to identify genetically superior animals. In conclusion, farmers should prioritise their time and resources to improve lamb survival and lamb growth for lambs born as triplets to mature ewes, or as any birth rank to ewe lambs. Lambs born to ewe lambs could be selected as replacement ewes, if they are heavy enough to be bred themselves at eight months of age. Lambs born to ewe lambs may be lighter than lambs born to mature ewes for their entire lifetimes, but have similar reproductive performance. There is genomic control of traits such as live weight and pregnancy occurrence in ewe lambs that needs further investigation, before genomics can be considered a practical tool for farmers when selecting their replacement ewes.
The effect of sire on growth and meat production of beef-cross-dairy cattle 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, 2021) Martín, Natalia de la Paz
Beef-cross-dairy cattle are the progeny produced by mating dairy-breed cows with beef-breed sires. Little is known about the performance of beef-breed sires for growth, carcass and meat quality traits when used to generate beef-cross-dairy cattle in pasture-based systems. Yet, beef-cross-dairy cattle make up around 30% of the finishing cattle in New Zealand, and so improving their performance would enhance the efficiency and productivity of the beef industry. The general aim of this study was to investigate the effect of sire on growth and meat production of beef-cross-dairy cattle in New Zealand. The specific objectives were: to evaluate live weight from 4 months of age until slaughter, carcass and meat quality traits of a selection of Angus and Hereford sires via progeny testing of beef-cross-dairy offspring grown on hill country pasture; to quantify the relationship between the performance of the beef-cross-dairy progeny and sires’ estimated breeding values (EBV) for growth and carcass traits; and to assess skeletal size and temperament measured within the first 200 days of life as predictors of carcass and meat quality traits for beef-cross-dairy cattle. Data from 1101 beef-cross-dairy calves born to 2-year-old or mixed-aged dairy-breed cows were used to analyse live weight, carcass and meat quality traits of 73 beef-breed sires (34 Angus and 39 Hereford). Meat samples were obtained for analysis in the laboratory from 326 progeny of 33 sires used via artificial breeding (AB) on mixed-aged dairy-breed cows. Progeny group means for live weight, carcass weight, eye muscle area (EMA), rib fat depth, marbling scores and intramuscular fat (IMF) of 29 Angus and 34 Hereford AB sires, were regressed against sire EBV within breed. Finally, 486 beef-cross-dairy calves had measurements of skeletal size and temperament evaluated as predictors of carcass and meat traits. The mean of the progeny group means for live weight was 118.6 kg at 131d, and increased to 503.6 kg at 800d. Mean of the progeny group means was 277.3 kg for carcass weight, 240.3 cm for carcass length, 73.6 cm2 for eye muscle area (EMA), 7.4 mm for rib fat depth, 0.91 for marble score, 3.05 for fat colour score and 3.01 for meat colour score. Sire affected (P<0.05) live weight of the progeny at all ages and all carcass traits, but few meat quality traits (fat yellowness b*, meat redness a* and yellowness b*, cook loss and shear force). Differences in live weight between the lightest and heaviest progeny group means increased from 19 kg at 131d to 90 kg at 800d, and there was a 46 kg difference in carcass weight between the heaviest and lightest sire tested. The coefficient of variation (CV) among sires for EMA was 5% and for measured rib fat depth was 19%, with no sire mean below 3 mm and most progeny (97%) grading “P” fat class. For marble scores, there was 35% CV between sires even though all progeny had low marble scores between 0 and 3. There were small sire effects for carcass length, cook loss and shear force (P<0.05). Meat and fat colour scores were not affected by sire, and although there were small sire differences in fat yellowness b*, no progeny carcasses were classified as being too yellow. Live weight of the progeny groups increased with sire EBV for live weight at 400, 600 and 800 days of age (between 0.24-0.43 kg increase in progeny live weight per extra kilogram of sire EBV), although sire EBV had no effect on the live weight of the progeny at 200 days of age (P>0.05). For the Hereford sires in this experiment, progeny carcass weight increased 0.27 kg and EMA 0.70 cm2 per extra 1 unit in sire EBV for each trait (P<0.05). For the Angus sires, progeny rib fat depth increased 6.9 mm, marble score 0.91 and estimated IMF 2.26% per extra 1 unit in sire EBV for each trait (P<0.05). Live weight at birth, 129d and 200d predicted future carcass size (P<0.05). In heifers, the accuracy of predictions of carcass weight from live weight were low to moderate (R2= 17 to 31%) and increased if live weight was combined with hip-height. In steers, live weight alone could predict carcass weight with moderate accuracy (R2= 39 to 48%). Accuracy of prediction for carcass weight of steers increased with age, or with combining live weight with body length at 0d, or with hip-width at 129d. Thicker cannon bones at birth also gave an indication of heavier carcasses for both heifers and steers. Cattle in this study were calm at 200d (mean exit velocity of 1.2 m/s and crush score of 1.4) and temperament did not influence production traits in this study. The data presented in this study indicated that using genetically superior beef-breed sires over dairy-breed cows increased the growth, carcass and meat production of their beef-cross-dairy progeny. Dairy farmers should consider BREEDPLAN EBV when selecting beef-breed sires to mate their dairy-breed cows, not only for positive calving outcomes but for achieving desirable and economically important carcass and meat quality traits. The beef cattle finisher should consider the calves’ potential for growth and fattening when purchasing beef-cross-dairy calves for beef production, by utilising both genetic and phenotypic live weight information.
Genetic parameters of body condition score (BCS) and effects of BCS and BCS change on ewe performance : 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, 2020) Vialoux, Isabel
Body condition score (BCS) is an important management technique that can be easily learnt and implemented on farm to determine the body condition of ewes. The industry recommended BCS is 3.0 to 3.5 at mating to ensure optimal production. Currently the average industry BCS is less than 3.0 and recent research suggests that the change in BCS may be more important for determining the subsequent production of the ewe. The objectives of this thesis were to examine the relationships between BCS and production through exploring the effects of genetic and phenotypic BCS and BCS change on productive performance. Records of BCS were obtained from Focus Genetics and New Zealand Merino flocks to determine the effect of BCS change on phenotypic production and estimate the genetic parameters of BCS. There was no increase in production for ewes above a BCS of 3.5, therefore, BCS of 3.0 to 3.5 should remain the target BCS for phenotypic production. Ewes that decreased phenotypic BCS between lambing and weaning were associated with greater production indicating these ewes had utilised their stored body fat to achieve high milk yields. The estimated heritabilities of BCS change were low indicating limitations in the ability to alter the shape of BCS profiles by selection. Heritability, genetic and phenotypic parameter estimations of BCS and production traits were performed on 9,585 dual-purpose ewes and 2,007 Merino ewes. The heritability of BCS in New Zealand dual-purpose sheep was found to be moderately heritable (0.16-0.30) and had a high genetic correlation between BCS measurements across the production year. The best time to record BCS for genetic selection was confirmed to be mating. Live weight and BCS are highly genetically correlated, therefore, it may be relevant to explore the inclusion of BCS in the selection criterion to ensure that BCS does not exceed the optimal range of 3.0 to 3.5. The results of this thesis indicate that observing BCS is a valuable tool and it would be possible to change the genetic potential for BCS with genetic selection. This information can be used to develop selection criteria for BCS.