The impact of sire beef genetic merit and concentrate supplementation strategy on phenotypic performance of dairy-beef steers

Beef from the dairy herd is becoming an important source of beef globally, but most dairy breeding objectives have typically not selected for beef production traits. Moreover, beef sires used in dairy herds are generally selected for ease of calving and short gestation, features known to be antagonistically correlated with carcass weight and conformation. Total merit breeding indexes collapse information from a series of (economically important) traits into a single rank per animal—one such type of total merit index is that which ranks beef bulls for mating to dairy females (i.e., a dairy-beef index). Such breeding objectives have not yet been validated in a controlled field study. In addition, there is a growing interest in identifying strategies to reduce slaughter age in pasture based dairy-beef systems. The objective of the present study was to quantify the benefits on dairy-beef steer performance from a combination of prudent sire selection using a dairy-beef breeding objective coupled with the strategic use of concentrate supplementation at pasture. Three genotypes were evaluated: 1) 66 animals produced from Angus sires in the top 40% of the Irish dairy-beef breeding objective (High Angus); 2) 92 animals produced from Angus sires in the bottom 60% of the Irish dairy-beef breeding objective (Low Angus); and 3) 75 animals from Holstein-Friesian (HF) sires. Each genotype was evaluated across one of three feed treatments (FT): 1) grass only (GO); 2) low concentrate (LC), and 3) high concentrate (HC). There was no association between genotype and feed treatment for animal growth. Results clearly demonstrated that progeny from sires excelling genetically in beef genetic merit outperformed progeny from low beef genetic merit sires for carcass weight. High Angus steers had a similar carcass weight (312.4 kg; P > 0.05) to HF steers (315.9 kg), with Low Angus steers having the lightest carcass (294.1 kg; P < 0.05). Nevertheless, HF steers were 84.5 d older than both Angus genotypes at slaughter (P < 0.05). Furthermore, supplementation during the second grazing season (the HC feed treatment) reduced the slaughter age of both Angus genotypes, but it had no effect on the slaughter age of HF steers. This study demonstrates the benefits of using high beef genetic merit sires in dairy herds to improve animal performance, whilst also demonstrating the potential to reduce slaughter age through supplementation.