Genetic parameters for growth, puberty, and beef cow reproductive traits in a puberty selection experiment

Abstract

A selection experiment to change reproductive traits in Angus cattle has been maintained for 14 years, with first calvings in 1985. Alongside an unselected control line, three lines were established, selected for increased age at puberty in heifers (AGE+ line), reduced age at puberty in heifers (AGE-line), or increased scrotal circumference (SC line). The last two lines were merged at the 1992 matings, with the revised objective of applying further selection in both sexes to reduce age at puberty in heifers. Dates at puberty in heifers from an average of 8 to 16 months of age and SC in bulls were recorded in all lines, along with the pregnancy rates (PR) and subsequent calving dates (CD) in heifers and all cow-age groups. Heritabilities of single-record SC, standardised age at first behavioural oestrus (SFO), and single-record CD were 0.41 ± 0.04 (repeatability 0.70 ± 0.01), 0.27 ± 0.04, and 0.09 ± 0.04 (repeatability 0.19 ±0.03), respectively. Genetic correlations of SC with SFO and CD were -0.25 ± 0.09 and -0.23 ± 0.15, respectively; SFO with CD 0.57 ± 0.17; and PR with SFO and SC-0.36 ±0.13 and 0.12 ± 0.11, respectively. The selection-line difference in PR over seven years (AGE-mean minus AGE+ mean), excluding yearling heifer matings, was 4.7 ± 2.1% (P < 0.05). Mean CD in the AGE-line was 3 days earlier than in the AGE+ line (P < 0.09). These correlation and selection-line results suggest that selecting for higher SC and earlier heifer puberty leads to earlier CD and higher PR.

Genetic variability in calving success in Aberdeen Angus cows under extensive recording

“…In a selection experiment assessing change in reproductive traits in Angus cattle, Morris et al (2000) found that heritability of pregnancy rate was 0.04 for cows, 0.08 for 2-year olds and 0.12 for yearlings. Johnston and Bunter (1996) analysed calving success without adjustment for the categorical nature of the trait, and reported a heritability estimate of 0.11.…”

Heredabilidad de características reproductivas de vacas Indubrasil.

“…En dicho estudio, los estimadores de heredabilidad para días abiertos fueron de 0,091 para vacas de diez o más partos y 0,197 para vacas de segundo parto. Por su parte, Morris et al (2000) reportaron que días abiertos fue 11% heredable en la raza Angus en un experimento de selección implementado para reducir la pubertad.…”

Responses of prolactin and hair growth to selection for age at puberty in Angus cattle

“…Since 1984/1985, the herd had been used in a divergent selection study, with the breeding objective being to change AP in heifers (Morris et al, 2000). The herd consisted of a line selected for increased pubertal age (AGE1) and another for reduced pubertal age (AGE2); these two lines grazed alongside a control unselected line.…”

“…Studies over the last 20 years at AgResearch have established that age at puberty (AP) in grazing heifers is inherited (heritability 0.26 6 0.03, as reported by Amyes and Morris, 2009), and responses of various correlated traits to selection for lower AP have been reported, including growth (Morris et al, 2000), carcass (Morris et al, 2006) and reproduction Amyes, 2005 and. With the management constraints involved in running the selection experiment, which included mating dates being at about the same time each year (and similarly calving dates), the expression of puberty was confounded with season.…”