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Title: Influence of cow breed type, age and previous lactation status on cow height, calf growth, and patterns of body weight, condition, and blood metabolites for cows grazing bahiagrass pastures

item Coleman, Samuel
item Chase, Chadwick - Chad
item RILEY, DAVID - Texas A&M University
item Williams, Mary - Mimi

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2016
Publication Date: 2/2/2017
Citation: Coleman, S.W., Chase, C.C., Riley, D.G., Williams, M.J. 2017. Influence of cow breed type, age and previous lactation status on cow height, calf growth, and patterns of body weight, condition, and blood metabolites for cows grazing bahiagrass pastures. Journal of Animal Science. J. Anim. Sci. 2017.95:139–153.

Interpretive Summary: Cow nutritional requirements constitute the largest expenditure for cow-calf operations. However, nutrition and the environment interact with animal genetics and affect efficiency of production. Research scientists with the USDA-ARS monitored cow performance and blood metabolites at monthly intervals over a two-yr period to determine how different breeds responded to two different nutritional packages for wintering in central Florida. The cow breeds were temperately adapted Angus, tropically adapted Brahman, and a novel tropically adapted Bos taurus breed, the Romosinuano, a native of Colombia imported from Venezuela. The two winter nutritional treatments were based on either rather poor quality bahiagrass hay supplemented with fortified molasses in the fall and with blackstrap molasses and soyhulls after calving in January. The other treatment was based on perennial peanut and bahiagrass mixed hay supplemented only with blackstrap molasses. At monthly intervals, body weight (BW) and body condition score (BCS) were monitored on three herds consisting of all three breeds maintained on three different research farms. Plasma concentrations of urea nitrogen (PUN), glucose, and non-esterified fatty acids (NEFA) were also measured on a subset of five cows per breed/treatment/farm subgroup. Results demonstrated the cyclic responses that occur in beef cattle through the grazing and calving seasons. Cows lost weight and condition at calving, recovered somewhat during the summer growing season, but most of the recovery occurred after weaning. Some sub-tropical forage systems may not fully support the needs of high producing cows throughout the cycle, so adequate measures should be taken to achieve adequate body condition for continuous rebreeding, especially among younger cows. While patterns of BW, BCS, PUN, and NEFA differed at times during the production cycle, the winter supplement system based on peanut hay resulted in heavier calves during the first year. However, little differences could be detected during the second year, or in percentage of cows pregnant. Brahman cows may be at higher risk for sustained nutritional status as indicated by sustained greater levels of circulating NEFA while nursing calves.

Technical Abstract: Economic analysis has revealed that in most parts of the country, the largest economic costs for cattle production are for winter feed. This study was initiated to evaluate the effect of two winter nutrition programs on three breeds of cows grazing bahiagrass pastures in central Florida. Data on 411 purebred cows over two years (Y) of either Angus, Brahman, or Romosinuano breeding (DB), were assigned to one of two nutrition regimes. Treatments (WT) began after weaning and were blocked over the three farms, each farm being a block. The treatments were: 1) peanut/bahiagrass hay fed at 2% BW from first frost and supplemented with heavy blackstrap molasses at 2.27 kg-1hd-1d (PBM) from weaning until end of breeding (~June 15); and 2) bahiagrass hay supplemented with urea-fortified molasses (16% protein equivalent) at 2.27 kg-1hd-1d from weaning until Jan 15 and then 4.5kg-1hd-1d of 50% heavy blackstrap molasses and 50% soyhulls (BMSH) until end of breeding. All cows rotationally grazed (moved twice weekly) bahiagrass pastures year-round. At monthly intervals, all cows were weighed (BW), measured at the hip (HH) scored for BCS, and blood samples collected by jugular puncture from 5 cows per DB/WT/block group for plasma urea N (PUN), glucose (GLU) and non-esterified fatty acids (NEFA). Data were analyzed on cows that calved with a statistical model that included fixed effects of Y, DB, cowage (CA), WT, month (M), farm, and whether the cow weaned a calf the previous year (WCLY). Cow was a repeated observation over months. Three-way interactions (CAxYxM, YxMxWCLY, YxMxWT, CAxMxDB, YxMxDB and MxWCLYxDB) were significant (P < 0.001) for BW and BCS. The interaction for CAxM was also significant (P < 0.05) for glucose, MxWT was important (P < 0.001) for NEFA, and M x DB was important (P < 0.01) for PUN, glucose, and NEFA. Important differences included: 1) greater BW and BCS for older cows compared to 3-yr old cows; 2) greater BW and BCS before calving for cows that were dry the previous year; 3) greater BW and BCS for cows fed PBM in Feb-Mar when supplements were fed; 4) PUN was generally greater in tropically adapted breeds; 3) GLU was greatest in Brahman, lowest in Angus, and intermediate in Romosinuano cows; and 4) plasma levels of NEFA escalated at calving and then declined, but Brahman cows maintained greater levels from calving until weaning than the other breeds.