Effect of protein level and bypass on milk production of cows fed total mixed rations

Author

Paula Joan Gaynor

Date of Award

8-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

M. J. Montgomery

Committee Members

J. P. Hitchcock, M. S. Younger, J. B. McLaren

Abstract

Feed costs represent an estimated fifty to sixty percent of total operating costs of most dairy operations. Cost of protein supplements has traditionally constituted a large percentage of total feed costs, which economically justifies research conducted with the purpose of evaluating the adequacy of low cost protein supplements in meeting dietary protein requirements for milk production.

Three experiments involving a total of 67 Holstein cows in the University of Tennessee Dairy Herd were conducted to determine the adequacy of pelleted protein supplement treated with inorganic water soluble salts (Trial 1), or supplemental dried brewer's grains (Trials 2a and 2b), in supporting milk production when fed with corn silage as a total mixed ration.

Trial 1 was conducted in cooperation with the Central Soya Feed Company of Decatur, Indiana, and involved 27 cows, 24 to 125 days postpartum, arranged in a switch-back design with three treatments and three experimental periods. Treatments consisted of varying concentrate composition of the total mixed ration as follows: 1) 18 % protein, untreated; 2) 15 % protein, treated with inorganic water soluble salts; and 3) 15 % protein, another (distinct) treatment of protein source with inorganic water soluble salts. Cows were fed ad libitum total mixed ration, plus 2.3 kg mixed alfalfa-grass hay per cow per day. Total mixed ration, corn silage, hay, milk, and blood samples were collected and analyzed.

Rations two and three contained substantially higher zinc and iron contents than ration one. Total mixed ration protein levels were 15.0 % (1), 12.6 % (2), and 13.0 % (3). Total dry matter intake, body weight iv change, and intake as a percent of body weight were not significantly different (p>.10) for the three rations. Milk, fat, and 4 % fat corrected milk, total solids, milk protein, solids-not-fat, and somatic cell counts were not different for the three rations. Plasma and milk zinc were higher for rations two and three (p<.05). The 15 % treated protein concentrate used in rations two and three supported milk production equally as well as the 18 % protein concentrate used in ration one.

In Trials 2a and 2b, the milk production and milk composition response to added dietary protein in the form of dried brewer's grains was evaluated. Ration one consisted of the standard milking herd ration composed of 2 parts corn silage and 1 part pelleted 16 % protein supplement blended and fed ad libitum, plus 5.6 kg mixed alfalfa-grass hay per cow per day. Ration two was the same as ration one, plus 2.3 kg per cow per day of dried brewer's grains added to the mixed rations. All cows received a mineral mixture of 1 % lime, 0.7 % MgO, dicalcium phosphate and trace mineral salt in the total mixed ration. Twenty cows within 2 weeks postpartum were assigned to either ration one or to ration two for a minimum of 11 weeks (Trial 2a) or 15 weeks (Trial 2b). All cows were offered 5.6 kg alfalfa-grass hay per day throughout Trials 2a and 2b.

Ration samples were available for Trial 2b only. For this reason, dry matter and protein contents of rations in Trial 2a were assumed to be the same as those found for samples collected in Trial 2b. Milk production and feed intakes and refusals were recorded daily.

Total dry matter intake, total protein intake and milk produced were significantly greater for the control ration, while fat corrected milk produced was not significantly different between the rations (Trial 2a). Contrary to Trial 2a, total dry matter intake, milk and fat corrected milk were greater (p<.05) for ration two in Trial 2b, while total crude protein intake was greater for ration one. Unaccounted for differences in ration composition, especially crude fiber content, or environmental differences may be responsible for the inconsistent results obtained between the two trials. The tendency for greater fat corrected milk production on ration two is consistent with the expectation that brewer's dried grains provide an increased supply of amino acids postruminally for absorption, thus enhancing the nutritional value of the total mixed ration consumed by the cow.

Recommended Citation

Gaynor, Paula Joan, "Effect of protein level and bypass on milk production of cows fed total mixed rations. " Master's Thesis, University of Tennessee, 1985.
https://trace.tennessee.edu/utk_gradthes/13995