Realized genetic selection differentials in Canadian Holstein dairy herds

Abstract

Estimated breeding values for a selection index, production, durability, health, and fertility traits for Canadian Holstein bulls and cows born from 1950 and 1960, respectively, were used to define and determine realized genetic selection differentials (GSD) and generation intervals along the 4-path model of genetic improvement and the variability among herds in realized GSD. The effects of some non-genetic factors on realized GSD were also determined. The mean generation intervals of the sire-to-bull (SB), dam-to-bull (DB), sire-to-cow (SC), and dam-to-cow (DC) pathways reduced, respectively, from 9.7, 7.5, 7.7, and 4.7 years in 1980 to 2.3, 2.5, 4.8, and 3.6 years in 2016. The realized GSD of lifetime performance index and 305-d milk, fat, and protein yields for the SB and DB paths were greater than those of the SC and DC, and realized GSD for DB were increasing for all production traits and the index after 2009. With the exception of daughter fertility (DF), we found zero to negative selection in the DC path for all the traits studied, due to the minimal opportunity for selection in that path. No clear trends were observed in realized GSD of SB, DB, or SC paths for mammary system, dairy strength, feet and legs, or herd life. The realized GSD for DF in the SB, DB, and SC remained largely negative, except after the early 2000s when positive realized GSD were observed in the SB and DB paths. The realized GSD for DF in the DC path remained positive throughout the period of the study, though mostly non-significantly different from zero, except for 2014 and 2015. Realized GSD for somatic cell score in the SB, DB, and SC paths showed increasing and favorable trends. Year of conception, housing system, agricultural region, and their interactions had significant effects on realized GSD of some traits in the SC and DC paths. We also observed considerable variations in realized GSD among herds. The population mean realized GSD and those of the top and bottom 10% of herds could serve as benchmarks that individual herds could use to monitor their past selection and make changes if they are not moving in the intended direction.

An insight into population structure and genetic progress of Argentinean Holstein cattle

“…The decrease for the SB path in the last 5 years found in this study was probably driven by the high influence of imported sires (mainly from the United States and CAN), and it might have contributed to the results of Δg obtained for the same period (Figure 6). However, the modest change seen in GI for the SC path is indicative of a mild interest for young genomic bulls (imported) in local dairy herds, contrary to the trend observed in other countries (Doublet et al, 2019; García‐Ruiz et al, 2016; Hagan et al, 2020; Scott et al, 2021).…”

“…For most of the considered period, the generation intervals of the fourth main paths of selection were in agreement with those commonly found in a dairy cattle population (Figure 4). Interestingly, shorter GI was detected approximately since genomic selection was implemented, as it happened in other countries (García‐Ruiz et al, 2016; Hagan et al, 2020; Scott et al, 2021). These changes are noticed particularly in the path of SB and to a less extent in SC and DB, with DC being the only path that remained fairly unchanged (Figure 4).…”

Efectos genéticos aditivos y no aditivos para características reproductivas en dialelo Holstein-Suizo Pardo en clima subtropical húmedo

“…Inclusive algunos autores indican que la raza SP y su F1 con Holstein tiene mejor rendimiento reproductivo y mayor adaptabilidad a condiciones tropicales (42) . Una de las posibles causas de la ineficiencia reproductiva de la raza Holstein se remonta a su selección histórica enfocada a su alta producción láctea (43,44) . El método base para su mejoramiento genético es la selección de individuos que sobrepasen el mérito productivo para dicha característica (45) , pero el uso incorrecto y generalizado de tecnologías de reproducción asistida, resulta en cientos o miles de crías de un solo padre (46) .…”

Developmental Programming of Fertility in Cattle—Is It a Cause for Concern?

“…Efforts by breeders to reverse negative trends in cow fertility caused by the previous overemphasis on production traits have led to small improvements in recent years. This follows greater inclusion of fertility and survival traits in genetic selection indices [ 232 , 233 ] and the increasing use of genomic selection for replacement heifers [ 234 , 235 ]. Poor fertility is, however, still a major concern and remains the main reason for involuntary culling in the dairy industry [ 236 ].…”