PSI-19 - Influence of cattle breed and forage type on organic dairy heifer performance.

Many breeds of dairy cattle exist, but questions remain about their relative performance within exclusively forage-based systems in the United States. This paucity of data is especially apparent in relation to heifer development, which is the second largest expense on most dairy farms. We evaluated the performance of prepubertal heifers from four different genetic backgrounds (“breeds”) within a rotational grazing system in the Intermountain West. For each of two 105-day grazing seasons, 24 dairy heifers from each of four different breeds [Holstein (HO), Jersey (JE), Holstein/Jersey crossbred (HJ), and Swedish Red/Holstein/Montbeliarde crossbred (SHM)] were randomly assigned to one of two pasture treatments that consisted of either grass only (MONO) or grass interseeded with the legume birdsfoot trefoil (BFT; MIX). Main effects of treatment and breed (and potential interactions) on heifer average daily gain (ADG), change in percent mature body weight (CPMBW), fecal egg count (FEC), rumen volatile fatty acids (VFA), and body condition scores (BCS) were evaluated. There was a significant effect of pasture treatment on ADG, with MIX heifers averaging 0.48 kg of gain/day, whereas MONO heifers averaged 0.29 kg/day (P < 0.0001). Change in BCS was significantly affected by treatment (P = 0.0012) and breed (P < 0.0001). Significant effects of treatment (P < 0.0001), breed (P = 0.0005), and treatment*breed (P = 0.0005) on CPMBW were also found. Treatment and breed had no effect on FEC or total rumen VFA content (P > 0.05). Overall, we found that Jerseys were able to gain a higher percentage of their mature body weight and lose less body condition while on pasture than heifers of other breeds. We also found that grazing BFT can have significant positive effects on ADG, BCS, and CPMBW. Further research is needed to more thoroughly evaluate the influence of heifer genetics (breed) on metrics of growth, health, reproductive performance, and production in pasture settings.