Masters Theses

Date of Award

8-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

J.W. Holloway

Committee Members

W.T. Butts, William Backus

Abstract

Milk and forage intake was measured on 158 Angus calves during a five year study beginning 1977. These calves were born in January through March, weaned in October, and grazed pastures of either high quality forage (red and white clover, Korean and Kobe lespedeza and tall fescue) or low quality forage (100% tall fescue). Milk intake estimates were performed monthly from April through October by the calf suckle technique. On June 26, July 31 and September 15 of each year, forage intake and digestibility trials were performed using the ADL (internal)/chromic oxide (external) indicator technique with trials containing a 5-day preliminary and 5-day collection period. Milk DE was estimated by total milk-out procedures during the 4th, 5th and 6th months of lactation. Forage DE and (milk DE) intakes for the June, July and September trials were 9.8 (4.5), 15.8 (4.0) and 19.8 (3.3) Mcal DE/day for calves grazing high quality pastures and 6.7 (3.9), 9.6 (3.4) and 14.8 (2.8) Mcal DE/day for calves on low quality pastures, respectively. An increase in milk DE intake was associated with a larger increase in weight gain for calves grazing low quality pastures than for calves grazing high quality pastures. Regarding calves on high quality pastures, as age increased, forage DE intake was associated with smaller increases in weight. All calves grazing low quality pastures were more dependent upon milk rather than forage for growth and performance.

In addition, the relationship of lactation curve shape to the pre-weaning performance of these same Angus calves was studied using the estimates of milk intake taken at various times during lactation. At weaning, calves were measured for height at withers, ultrasonic fatness at the 12th rib and weight. Milk intake for each calf was described by the function milk production = Ae-cttb where A, b and c are constants estimated by evaluating these functions, t is a time value and e is the logarithmic function. Peak lactation occurred at 80 and 68 days for the calves on high and low quality pasture, respectively. Average milk intake explained 53% of the variation in weaning weight for calves on low quality pastures whereas, for calves on high quality pastures, it explained only 33% of the variation in weaning weight. When milk intakes at birth, peak lactation and weaning were adjusted for average milk intake, they explained 15 to 40% of the variation in weaning weight that was not explained by average milk intake. Generally, shape of the lactation curve was more important for the growth of the calves on low quality pastures than for calves on high quality pastures. Desirable curves in this study were determined to be associated with high peaks and low persistence.

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