Masters Theses

Date of Award

8-1982

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

J.B. McLaren

Committee Members

D.O Richardson, R.N. Heitmann

Abstract

Thirty days before they were marketed, feeder calves were measured, sampled and allotted to preconditioning or market-management systems at the farms of Tennessee and Kentucky feeder-calf producers during each fall marketing season (1977-1978). Body measurements were weight (WT). height (HT), length (LEN). depth (DP), width (WD) and fat thickness over the 12th rib (BF). Rumen samples were taken by the tube method from intact steers and volatile fatty acids (VFA), protozoa concentrations and pH were determined. Rumen liquid volume and in vitro gas producing potential of the fluid (GPP) were estimated. Principal component indices describing general calf size (SIZE) and calf shape (SHAPE) were calculated. Calves from two farms were used to study the relationship of SIZE and SHAPE to rumen function at FO before weaning. Rumen volume was correlated with WT, WD, HT, DP and SIZE. Acetate was related (P<.01) to WT and BF. Depth and HT were the only individual body measurements that explained a large portion of the variation in protozoal concentration. Acetate and total VFA increased linearly (P<.10) as SIZE increased. Similar trends were observed for acetate, butyrate and higher VFA. The relationship of acetate and total VFA to SHAPE was curvilinear. Similar curvilinear trends were observed in the relationship of Spirotricha and total protozoal concentrations with SHAPE.

At FO the calves were randomly assigned to one of the three following market-management systems: 1) weaning and feeding a concentrate diet during the last 30 days before marketing and feeding hay at the orderbuyer barn (PW) and 2) allowing the calves to graze pasture with their dams during this period and feeding hay (NI) or a 50% concentrate diet at the orderbuyer barn (HE).

Rumen characteristics were measured at the beginning and end of the market phase. In general, calf size was related to changes in the total rumen protozoal concentration and to changes in protozoa subclass and genera populations. Calf shape was generally related to changes in volatile fatty acid concentrations. The changes in VFA concentrations were generally smallest in PW calves and the relationship of these changes to shape was greatest in HE calves. The relationship of protozoal changes to shape was more varied among the three groups (NI, HE, and PW calves) and were more difficult to explain than the relationship with size. Significant relationships of calf size and shape to change in rumen characteristics of weanling calves and changes in rumen characteristics during market were observed. This relation ship was affected by market-management or preconditioning system to which the calves were subjected. In general, VFA concentrations and market changes were related to calf size and protozoal concentrations and market changes were related to calf shape.

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