Pure-breeding with sexed semen and crossbreeding with semen of double-muscled sires to improve beef production from dairy herds: Factors affecting heifer and cow fertility and the sex ratio

摘要

Using sexed semen to produce purebred replacementheifers makes it possible to mate a large proportionof dairy cows to double-muscled sires and to quantitativelyand qualitatively improve beef production andincrease the income from dairy herds. Net profit firstdepends on changes in the farm’s overall fertility rate.The objective of this study was to analyze the conceptionrate in herds using a combination of conventionaldairy semen (for pure- and crossbreeding), X-sorteddairy semen (to produce purebred replacement heifers),and conventional beef semen (for terminal crossbreeding).Data were obtained from 50,785 inseminations of15,580 dairy cows (78% Holstein-Friesian, 15% BrownSwiss, 2% Simmental, and 5% crossbreds) from 106dairy farms (average milk yield 35.1 ± 9.4 kg/d, with3.76 ± 0.83% fat and 3.32 ± 0.39% protein contents).To account for the main potential confounders, weused separate generalized linear mixed-effects modelsfor cows and virgin heifers. The results showed thatthe odds ratio of conception improved (1.00 to 1.34)with an increase in the average milk yield of the herdbut worsened (1.12 to 0.70) with an increase in themilk yield of individual cows within herd. The summermonths showed a strong reduction in the odds ratioof conception in cows (0.56 in July and August) butnot in virgin heifers. Multiparous cows had a lowerodds ratio of conception (0.85) than primiparous cows(1.00). The order of insemination did not affect thefertility of the cows or heifers, whereas the odds ratioof conception improved with advancing lactation (1.00to 2.12). The Simmental cows were more fertile thanHolstein-Friesians (1.37 vs. 1.00), whereas the fertilityof the heifers was not affected by breed. Taking all thesepossible confounders into account simultaneously, inpure-breeding the odds ratio of conception using sexedsemen did not differ from that using conventional dairysemen in cows (0.90 vs. 1.00) or in virgin heifers (0.95vs. 1.00). However, crossbreeding using conventionalbeef and dairy semen improved the odds ratio of conception(1.10 and 1.17, respectively) in cows (1.37 usingbeef semen) and heifers (1.25 using dairy semen). Theproportion of newborn heifer calves was ≥90% usingsexed dairy semen. The combined use of sexed semen,especially on heifers, to produce purebred replacementfemales and beef semen to produce terminal crossbredcalves was shown to have the potential to increase overallherd fertility, which could be further improved usingsexed dairy semen to produce dairy crossbreds insteadof purebred replacement heifers.