Department of Agronomy, Food, Natural Resources, Animals and Environment (DAFNAE), University of Padova (Padua), 35020 Legnaro (PD), Italy.
Department of Animal Science, Food and Nutrition (DIANA), Catholic University, 29122 Piacenza, Italy; Italian Association of Breeders (AIA), 00161 Rome, Italy.
J Dairy Sci. 2020 Jun;103(6):5246-5257. doi: 10.3168/jds.2019-17932. Epub 2020 Apr 16.
Using sexed semen to produce purebred replacement heifers makes it possible to mate a large proportion of dairy cows to double-muscled sires and to quantitatively and qualitatively improve beef production and increase the income from dairy herds. Net profit first depends on changes in the farm's overall fertility rate. The objective of this study was to analyze the conception rate in herds using a combination of conventional dairy semen (for pure- and crossbreeding), X-sorted dairy semen (to produce purebred replacement heifers), and conventional beef semen (for terminal crossbreeding). Data were obtained from 50,785 inseminations of 15,580 dairy cows (78% Holstein-Friesian, 15% Brown Swiss, 2% Simmental, and 5% crossbreds) from 106 dairy farms (average milk yield 35.1 ± 9.4 kg/d, with 3.76 ± 0.83% fat and 3.32 ± 0.39% protein contents). To account for the main potential confounders, we used separate generalized linear mixed-effects models for cows and virgin heifers. The results showed that the odds ratio of conception improved (1.00 to 1.34) with an increase in the average milk yield of the herd but worsened (1.12 to 0.70) with an increase in the milk yield of individual cows within herd. The summer months showed a strong reduction in the odds ratio of conception in cows (0.56 in July and August) but not in virgin heifers. Multiparous cows had a lower odds ratio of conception (0.85) than primiparous cows (1.00). The order of insemination did not affect the fertility of the cows or heifers, whereas the odds ratio of conception improved with advancing lactation (1.00 to 2.12). The Simmental cows were more fertile than Holstein-Friesians (1.37 vs. 1.00), whereas the fertility of the heifers was not affected by breed. Taking all these possible confounders into account simultaneously, in pure-breeding the odds ratio of conception using sexed semen did not differ from that using conventional dairy semen in cows (0.90 vs. 1.00) or in virgin heifers (0.95 vs. 1.00). However, crossbreeding using conventional beef and dairy semen improved the odds ratio of conception (1.10 and 1.17, respectively) in cows (1.37 using beef semen) and heifers (1.25 using dairy semen). The proportion of newborn heifer calves was ≥90% using sexed dairy semen. The combined use of sexed semen, especially on heifers, to produce purebred replacement females and beef semen to produce terminal crossbred calves was shown to have the potential to increase overall herd fertility, which could be further improved using sexed dairy semen to produce dairy crossbreds instead of purebred replacement heifers.
利用性控精液生产纯种后备母牛，可使大部分奶牛与双肌种公牛配种，并从数量和质量上提高牛肉产量，增加奶牛群的收入。净利润首先取决于农场整体繁殖率的变化。本研究的目的是分析使用常规奶牛精液（用于纯种和杂交）、X 分选奶牛精液（用于生产纯种后备母牛）和常规肉牛精液（用于终端杂交）组合的牛群的受孕率。数据来自 106 个奶牛场的 50785 次 15580 头奶牛（78%荷斯坦弗里森牛、15%瑞士褐牛、2%西门塔尔牛和 5%杂交牛）的配种情况（平均产奶量为 35.1±9.4kg/d，乳脂率为 3.76±0.83%，乳蛋白率为 3.32±0.39%）。为了考虑主要的潜在混杂因素，我们分别为奶牛和初情期后备母牛使用了广义线性混合效应模型。结果表明，随着牛群平均产奶量的增加，受孕率的优势比提高（1.00 至 1.34），但随着牛群中个体奶牛产奶量的增加，受孕率恶化（1.12 至 0.70）。夏季月份，奶牛的受孕率优势比（0.56 为 7 月和 8 月）大幅下降，但后备母牛不受影响。经产牛的受孕率优势比（0.85）低于初产牛（1.00）。输精顺序不影响奶牛或后备母牛的繁殖力，而随着泌乳期的推进，受孕率优势比增加（1.00 至 2.12）。西门塔尔牛比荷斯坦弗里森牛更具繁殖力（1.37 比 1.00），而后备母牛的繁殖力不受品种影响。同时考虑到所有这些可能的混杂因素，在纯种繁殖中，使用性控精液的奶牛（0.90 比 1.00）或后备母牛（0.95 比 1.00）的受孕率优势比与使用常规奶牛精液没有差异。然而，使用常规肉牛和奶牛精液进行杂交可提高奶牛（使用肉牛精液时为 1.10，使用奶牛精液时为 1.17）和后备母牛（使用奶牛精液时为 1.25）的受孕率优势比。使用性控奶牛精液生产纯种后备母牛和使用肉牛精液生产终端杂交牛的比例均≥90%。研究表明，联合使用性控精液，特别是对后备母牛，生产纯种后备母牛和肉牛精液生产终端杂交牛，有可能提高整体牛群的繁殖力，使用性控奶牛精液生产奶牛杂交牛而不是纯种后备母牛，可能进一步提高繁殖力。
