Date of Award:

12-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

S. Clay Isom

Committee

S. Clay Isom

Committee

Kara J. Thornton-Kurth

Committee

Kerry A. Rood

Committee

Blair Waldron

Abstract

There are many different breeds of dairy cattle in the United States. However, research on how well heifers from different breeds develop when grazing pasture alone has not been done in the United States. This data can be very important for dairy producers, since developing heifers is the second largest expense on most dairy farms. In this study, we evaluated the performance of pre-pubertal heifers from four different 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 VikingRed/Holstein/Montbeliarde crossbred (PRO)] 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). Within our study we looked at the effects of BFT and the differences between breeds for the following: 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). We saw that BFT significantly increased ADG for all breeds. Heifers which grazed the MIX treatments averaged 0.48 kg of gain/day, whereas heifers on MONO pastures averaged 0.28 kg/day. Overall changes in BCS were significantly affected by both the differences in treatment and breed of the animals. When CPMBW was analyzed, heifers grazing BFT pastures had greater increases as well as there being a difference in breed with JE heifers outperforming other breeds. The different treatments did not cause any significant differences in FEC or total VFA concentrations. Overall, we found that Jerseys were able to gain a higher percentage of their mature body weight and maintain their body condition better, while grazing, than heifers of other breeds. We also determined that grazing BFT can have noticeable positive effects on ADG, BCS, and CPMBW. For dairy producers who graze their animals, it is important for them to realize the benefit of planting BFT in their pastures and the benefit seen in our study of using Jersey heifers, which had better increases in their mature body weight when compared to other breeds. This knowledge can help dairy producers become more efficient and profitable.

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