Date of Award

12-2015

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

John T. Mulliniks

Committee Members

Arnold M. Saxton, Renata Nave, Justin Rhinehart

Abstract

The beef cattle industry tends to focus on selecting production traits with the purpose of maximizing cow-calf performance. One such trait is milking ability, which is considered the primary influence on weaning weight of the calf. But, it can also have a negative effect on cow reproductive efficiency and cost of production. Therefore, the objective of this study was to determine the effect of actual milk yield on reproductive performance, circulating blood metabolites, and calf performance in beef cows in Tennessee. Data were collected from 239, 3- to 9-yr-old Angus sired beef cows from 3 research centers across Tennessee. On approximately d 58 and 129 postpartum, 24-hr milk production was measured with a modified weigh-suckle-weigh technique using a milking machine. Subsamples of milk were collected for analysis of milk components. Milk yield data were used to classify cows on actual milk yield as High (≥ 10 kg/d), Moderate (8-9 kg/d), or Low (/d). Cow BW and BCS were collected weekly at each location through breeding. Calf BW was recorded at birth, mid-weight for an adjusted 58-d, and weaning BW for an adjusted 205-d. At d 58 and 129 of postpartum, milk yields were different (P < 0.001) among the treatment groups. Milk fat, protein, and solids-non-fat (g/d) were influenced (P < 0.001) by milk yield. However, milk lactose was not influenced (P = 0.82) by milk yield. Cow BW at the beginning of the study and at the end of breeding were different (P < 0.05) among milk production groups. Cow BCS were different after parturition, and pre- breeding (P ≤ 0.05). AI pregnancy rates and overall pregnancy rates were not different (P ≥ 0.21) across the individual milk groups. Calf BW at 58-d and 205-d of age (P < 0.001) was influenced by milk production level of their dams. Results indicate that increased milk production in beef cows has the potential to increase calf weights at weaning. However, selection for milk production in this management environment could be discounted to decrease to nutrient demands of lactation and maintain productivity.

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