Jason A. Archer

The expansion of the New Zealand dairy industry has increased the number of lower‐value surplus calves. A value‐add mitigation strategy is integrating them into the beef market. This study investigated the genetic association between growth traits recorded in the Beef + Lamb New Zealand's Dairy‐Beef and the Beef Progeny Test to estimate the genetic correlation between dairy weaning, 200‐, 400‐, and 600‐day weights in beef‐on‐dairy and beef cattle. Single‐trait and bivariate animal models were used to estimate (co)variance components for heritabilities, genetic and phenotypic correlations between traits within the beef‐on‐dairy and beef progeny tests. Estimated heritabilities for beef‐on‐dairy cattle were similar to those for beef cattle. Genetic correlations for growth traits within and across tests were moderate to strong (between 0.46 and 0.99). Phenotypic correlations between traits tended to be lower than the genetic correlations within‐test (0.36 to 0.82). The results indicate that data collected in beef system can usefully inform predictions of growth performance in beef‐on‐dairy systems but that it may not always be appropriate to treat similar measures as the same trait in a genetic model. However, the opportunity exists to combine beef and beef‐on‐dairy data to, simplify breeding, reduce costs and improve genetic merit of beef‐on‐dairy calves.

Research has shown that enhancing finishing performance in beef cows is feasible; however, any adverse impact of selection strategies for finishing performance on the performance of the maternal herd should be taken into account. The aim of this research was to examine the inheritance of growth, ultrasound and carcass traits in finishing beef cattle and to evaluate their correlations with maternal performance traits. Data were collected from a nationwide progeny test on commercial New Zealand hill country farms comprising a total of 4473 beef cows and their progeny. Most finishing traits were moderately to highly heritable (0.28–0.58) with the exception of meat or fat colour and ossification (0.00–0.12). Ultrasound scan traits had high genetic correlations with corresponding traits measured at slaughter (r_g = 0.53–0.95) and may be used as a selection tool for improved genetic merit of the beef carcass. Fat content determined via ultrasound scanning in the live animal or at slaughter in finishing cattle is positively genetically correlated with rebreeding performance (r_g = 0.22–0.39) in female herd replacements and negatively correlated with mature cow live weight (r_g = −0.40 to −0.19). Low-magnitude associations were observed between the genetic merit for carcass fat traits with body condition in mature cows.

Maternal performance is a major driver of profitability in cow-calf beef cattle enterprises. The aim of this research was to evaluate the inheritance of maternal performance traits and examine the intercorrelation among reproduction, live weight, hip height, body condition and maternal contribution to calf weaning weight in 15-month-old heifers, 2-year-old cows and mature cows in New Zealand beef herds. Data were collected on a total of 14,241 cows and their progeny on five commercial New Zealand hill country farms. Heritabilities were low for reproductive traits in heifers and mature cows (0–0.06) but were greater in 2-year-old cows (0.12–0.21). Body condition scores were lowly (0.15–0.26) and live weights (0.42–0.48) and hip heights (0.47–0.65) highly heritable in heifers, 2-year-old cows and mature cows. Results indicate that 2-year-old cows with higher genetic potential for rebreeding ability may have greater genetic merit for live weight, hip height and body condition as heifers (r_g = 0.19–0.54) but are unlikely to be larger cows at maturity (r_g = −0.27–−0.10). The maternal genetic effect on weaning weight had a heritability of 0.20 and was negatively genetically correlated with body condition score in lactating cows (r_g = −0.55–−0.40) but positively genetically correlated with rebreeding performance (r_g = 0.48).

Data on 914 Angus heifers and their calves that had been selected for yearling growth rate (from birth to 1 year of age) were used to ( i ) evaluate the effect of dystocia on subsequent cow and calf performance, ( ii ) identify factors influencing dystocia, and ( iii ) develop and validate equations for predicting dystocia. Records on heifers born in the high, control, and low growth selection lines from 1975 to 1990 and their calves were used. Calving was classified as normal (no assistance), with a code of 0, or difficult (requiring assistance), with a code of 1. The incidence of dystocia was 4.5%, 9.7%, and 6.2% in the high, control, and low lines, respectively, with the difference between the high and control lines being significant ( P < 0.05). Dystocia resulted in a significant reduction in calf survival to weaning (97% for normal v . 85% for difficult calvings). Of all the calving and pre-calving traits studied, the ratio of calf birth weight to heifer weight accounted for the highest variation in dystocia in the control (19.6%), low (15.2%), and high (5.4%) lines. The total variation explained by models generated by stepwise regression and discriminant analyses ranged from 5.4% to 36.8%. Prediction equations developed by discriminant analysis using traits measured prior to calving had high accuracy of predicting normal calvings (72.6%–90.3%), when tested on independent data sets. However, the sensitivity (ability to identify those heifers having difficult birth) of the equations was low (0%–40%). These results imply that the approach to be used to reduce dystocia and minimise its effects is to develop an overall management strategy involving both planning of mate selection at joining and supervision at calving.