Genetic correlations among weight and cumulative productivity of crossbred beef cows1

Abstract

Mature weight of beef cows in the United States has been increasing as a correlated response to selection for calf growth. Unfavorable genetic correlations between cow weight and various measures of female fertility, stayability, and lifetime production suggest declining cow productivity might also be expected as a correlated response to growth selection. National cattle evaluations, however, show increasing trends for stayability and sustained fertility. Random regression (RR) models were employed to further examine genetic relationships among cow weight and productivity, and to assess cumulative productivity traits observed throughout cows' productive lives. Records were from 13,707 females born in the Germplasm Evaluation (GPE) project and mated to calve first as 2-yr olds. Weights observed at pregnancy testing (n = 65,086) and calf production from each exposure to breeding (n = 71,583) were included in uni-and bivariate RR analyses. Production following each breeding season was added to previous production to obtain cumulative production records for each season that the female was exposed to breeding. Zero was added if the cow failed to produce after a breeding season. The number of pregnancies, calves born and calves weaned, as well as age and weight of weaned calves, were accumulated. Projected age-specific heritability (h 2 ) estimates for cumulative production were low (<0.1) at age 2 but increased with age (0.12 to 0.26 at age 6; 0.32 to 0.48 at age 10). Estimated h 2 for cow weight were high, fluctuating between 0.6 and 0.7 from ages 2 through 10. Genetic correlations (r g ) were positive among all ages within each trait. Between ages 3 and 9, estimated r g were negative between cumulative weaning productivity and cow weight. The correlations were usually weak enough (<−0.2) that small correlated declines from following yearling weight trends might be overcome by culling females after their first reproductive failure. More noticeable increases might be realized by selection among sires with EBV based on productivity of several daughters. The RR EBV for cow weight and cumulative weight weaned represent major sources of variation in cow costs and income, and can be incorporated into economic selection indexes to project differences in cow profitability and value at any age. The RR approach utilizes all available records, enabling later productivity to be projected from observations on young cows.

Genetic Basis of Blood-Based Traits and Their Relationship With Performance and Environment in Beef Cattle at Weaning

“…Heritability (h 2 ) estimates in the present study are in line with what is generally reported in the literature (Kitchenham and Rowlands, 1976;Bourdon and Brinks, 1982;Rowlands et al, 1983;Arnold et al, 1991;Bullock et al, 1993;Bennett and Gregory, 1996;Phocas and Laloë, 2004;Wright et al, 2014;Mpetile et al, 2015;Snelling et al, 2019). Heritability estimates (h 2 ) for white blood cell traits by Leach et al (2013) ranged from 0.28 to 0.50, confirming the findings of the present study, with the only exception of MO which had a heritability estimate (h 2 ) of 0.11 and 0.01 for Bayesian and frequentist approaches respectively, which in both cases are lower than the estimates previously reported by Leach et al (2013) that ranged from 0.21 to 0.39.…”

Breeding Sustainable Beef Cows: Reducing Weight and Increasing Productivity

“…Cow weight at pregnancy test (CW) and cumulative weight weaned (WtW) records were obtained on 6211 genotyped females from GPE Cycles VII [ 18 ] and VIII [ 19 ] and the current 18-breed continuous GPE sampling [ 20 ], following procedures developed for random regression analyses of these traits [ 9 ]. Briefly, a record for WtW was created each time a female was exposed to breeding, starting with their initial breeding to calve as a two-year-old.…”

“…The extension of stayability to evaluate cow weight and cumulative cow productivity [ 9 ] under a restricted breeding season provides refined tools to breed for sustainability. These evaluations predict the most and least productive cows, and weight indicates feed requirements [ 10 ] and methane emissions [ 11 ].…”

“…These evaluations predict the most and least productive cows, and weight indicates feed requirements [ 10 ] and methane emissions [ 11 ]. Cow weight evaluations [ 9 , 12 ] are also considered in developing a herd suitable for managed grazing prescribed for sustainable beef production [ 1 , 2 , 3 , 4 ]. Managed grazing can protect and improve land resources and increase carbon sequestration [ 13 ].…”

Number of Calving and Its Relationship with Productive Indicators in Nelore Cows

“…Longevity is the most important functional trait in cattle selection worldwide [6]. There are previous works where they show negative correlations between the weight of the cow and the stability or the useful life of the same; this made that the main associations of meat breeds in the USA report on the permanence or fertility of cows [7]. Some of the fertility measures used in beef cow evaluations, such as length of productive life, interval between the first and second calving, and calves born at a specific age, should be incorporated into analyses of the entire life of the cow [8].…”