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

Abstract

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.