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Genetic correlations were estimated between pubertal traits of males or females and yearling or lifetime pregnancy rate (PR) in beef cows, using 269 paternal half-sib groups. Lifetime PR was recorded from up to 5 mating/calving years for each cow. The genetic correlations between age at first oestrus (AFO) or standardised age at first oestrus (SFO) and yearling PR were −0.30 ± 0.26 and −0.67 ± 0.44, whilst corresponding estimates with lifetime PR were −0.29 ± 0.26 and −0.76 ± 0.68. For scrotal circumference (SC), genetic correlation estimates with yearling PR were 0.53 ± 0.66 and with lifetime PR 0.34 ± 0.40. The data generally supported the concept of a favourable genetic correlation between pubertal traits (higher SC or lower AFO and SFO) and lifetime PR.

A total of 3768 calves and 4950 cow mating-years were involved in a study of heterosis retention. Crosses included first and subsequent inter-crosses between Angus and Hereford breeds as far as the fifth calf generation (F1, F2,…F5), back crosses (B1) using both F1 sires and F1 dams, and rotation crosses as far as the fifth calf generation (R2, R3, R4 and R5). Records collected were calf traits to the yearling stage, cow reproduction and maternal traits, and steer carcass data. Effects were estimated for 27 breed types for calves and 23 for cows. Breed type effects were then replaced by multiple regression coefficients for genetic effects including: an average individual (Angus) breed effect (gI), average maternal (gM) and average grandmaternal (gMG) breed effects, individual (dI), maternal (dM) and paternal (dP) dominance effects, and epistatic effects. From these, individual (hI) and maternal (hM) heterosis and other parameters were derived. For the Angus breed, gI was generally negative and gM positive for direct calf weights and cow weight; gI was positive for calf weaning weight (WW) as a maternal trait. The Angus breed was superior to the Hereford for net reproduction, productivity (weight of calf weaned per cow mated) and an efficiency ratio (productivity/average cow weight). Relative to the average of the purebreds, the superiorities of F1, F3 to F5, and R4 animals were respectively 2.1, 3.2 and 5.0% for birth weight, 6.5, 3.7 and 7.9% for yearling weight, 6.7, −2.2 and 3.4% for cow weight, 10.3, 0.7 and 11.7% for calf WW as a maternal trait, 7.4, −1.3 and 5.7% for number of calves weaned per cow mated, 19.4, 1.0 and 18.4% for productivity, and 11.2, 2.1 and 14.0% for the efficiency ratio. For calf traits and cow weight, dM and hI were generally significant and positive (except negative for calving date), whilst only hI was generally significant for calf weights as maternal traits. For the reproductive traits, the trends were for hI to be positive, but standard errors were large. For carcass traits, the interbreds and rotation crosses were generally like the heavier, fatter (i.e. Hereford) purebred. Overall, for productivity and the efficiency ratio, the rotation crosses (especially R4) were superior to the purebreds but generally not to the Fls, whilst the interbreds were similar to the purebred average.

Records from a crossbreeding experiment were analysed to estimate the genetic correlation between scrotal circumference in bulls and pubertal traits in heifers, using paternal half-sib relationships. There were 234 sire groups in common. Bull and heifer calves were selected at random at weaning to comprise about five and six potential replacements respectively per sire group. In total 1307 bulls (born in 1980–1985) were each recorded for scrotal circumference in May (8 months of age), August and October, and 1302 heifers (born in 1981–1985) were checked for puberty for a 7-month period (using chinball harnesses on bulls) from about the beginning of May until mid-December. The pubertal traits in heifers were age at first oestrus (AFO), standardised age at first oestrus (SFO) and weight at first oestrus (WFO). Live weights were recorded monthly on heifers and WFO was interpolated from these weights. The heritabilities and genetic correlations were estimated using restricted maximum likelihood. Heritabilities for scrotal circumference were 0.50 ± 0.11, 0.33 ± 0.10 and 0.29 ± 0.10 in May, August and October respectively (0.29 ± 0.07 for all ages combined), whilst those for AFO, SFO and WFO were 0.33 ± 0.12, 0.32 ± 0.10 and 0.40 ± 0.13, respectively. Genetic correlations between scrotal circumference and heifer puberty traits averaged −0.39 ± 0.22 for AFO, −0.19 ± 0.20 for SFO and −0.39 ± 0.20 for WFO.