Lower replacement costs, greater average milk output, and fewer replacement heifers are all connected with increased lifespan. Because longevity statistics are collected late in life, stayability, defined as the chance of surviving from birth to a specific age, may be used as an alternative metric. The purpose of this research was to investigate the impact of various type features, inbreeding, and production level on the stayability of Jersey cows at various ages, as well as to track changes over time. The data set included 460,172 to 204,658 stayability records for survival from birth to 36, 48, 60, 72, or 84 months of age, depending on the duration of the opportunity period. Threshold models were used to analyse the stayability features, which included explanatory factors such as various type attributes, inbreeding coefficient, and within-herd production level. Stayability trait heritability estimates varied from 0.05 (36 mo) to 0.22 (84 mo). As predicted, the likelihood of survival declined with age. Regardless of age or the type attribute tested, highly productive cows were more likely to survive than their poor-producing peers. Our data show that farmers’ selection choices tend to penalise low productivity in the beginning and reward good production later on. Inbreeding reduced the likelihood of survival, particularly when inbreeding coefficients surpassed 10%, and this effect was most obvious at 48 months of age or later. Some personality features, such as size and foot angle, have minimal influence on survival. Other type attributes, such as strength, dairy shape, rump breadth, and rear legs, had a better likelihood of survival at intermediate scores, while fore udder attachment, rear udder height, udder depth, and final score had a lower probability of survival at higher scores. Finally, our findings show that the chance of survival has reduced over the previous decade, most likely owing to a larger number of available heifers and, as a consequence, increased culling rates.
Longevity in dairy cattle is linked to lower replacement costs and higher average milk output. Farmers cull low-producing cows willingly for economic reasons in order to increase farm profitability. Poor reproduction, injuries, and diseases, on the other hand, might require the forced culling of productive animals, increasing veterinary expenses and decreasing farm profitability. In addition to milk output, linear type features and inbreeding may be linked to culling, either directly or indirectly via connections with disease, injury, or infertility. Stayability may be used as an alternate metric to longevity since it is assessed late in life. Small heritability estimates for STAY36, STAY48, STAY60, STAY72, and STAY84 in our analysis imply that selection for enhanced stayability would result in gradual genetic gains. Kern et al., 2014 discovered similar findings when using a threshold model to assess the lifetime of Holstein cattle. Productive life is used to assess the duration from first calving till culling in the lifetime net merit index (NM$) published by the Council on Dairy Cattle Breeding (Cole et al., 2021), and it gets a relative economic focus of approximately 20% in Jersey cattle (VanRaden et al., 2021). As a result, despite the possibility of sluggish genetic improvement owing to low heritability, selection for longevity is critical in US dairy cattle. Furthermore, since it is substantially and favourably connected with survival until later ages, stayability till younger ages may be a suitable selection criteria for longevity.
Through its correlation with the occurrence of certain illnesses and injuries, type features are indirectly associated to lifespan. Poor foot and limb conformation, for example, has been linked to higher lameness genetically (Khansefid et al., 2021). In earlier research, however, the connection between chance of survival and foot angle and rear leg scores in Jersey and Holstein-Friesian cows was minimal (Caraviello et al., 2003; Williams et al., 2022a). Our research discovered a little link between STAY60 and foot angle score, while rear leg score seemed to have greater impacts on survival, with reduced survival at both extremes. Rump angle scores with low or high pins may be connected to calving problems, which might increase the likelihood of culling (Sewalem et al., 2004), and our findings revealed that cows with an intermediate rump angle were more likely to live to 60 months of age. Poor teat placement has been linked to lower machine milking efficiency and a higher incidence of subclinical mastitis (Singh et al., 2017), and our study found that cows with more central teat placement, and thus intermediate scores for front and rear teat placement (side and rear views), had a higher chance of survival. Other udder-related type features, including as udder depth, udder cleft, fore udder attachment, rear udder height, and rear udder breadth, are linked to variances in milk production and injury sensitivity. Among the type characteristics evaluated, Caraviello et al. (2003) found that udder features were the most significant predictors of lifespan in Jersey cattle. Similar to the current research, the authors reported a significant danger of culling for animals with low scores for those features, with declining rewards in survival likelihood as type scores neared their maximum. In earlier investigations with Holstein and Jersey cattle, height was shown to be the least relevant feature in terms of survival (Caraviello et al., 2003; Sewalem et al., 2004). Notably, within-herd ranking for milk production has a considerable effect on culling choices, and its relevance in comparison to type features seems to have risen over time. Cows with high final scores had identical chances of surviving in the past, regardless of milk production level. Cows with poor milk output, although having excellent type ratings, seem to be removed from the herd in recent years.
owing to increased homozygosity, inbreeding depression has significant direct consequences on performance, which may lead to greater culling owing to poor production, longer calving intervals, lower conception rates, and higher somatic cell scores (Doekes et al., 2019). Caraviello et al., 2003 found that animals with inbreeding coefficients more than 7% had a higher risk of culling, and they found a roughly linear association between risk of culling and inbreeding coefficients. According to Sewalem et al. (2006), Jersey cows with inbreeding coefficients more than 12.5 were around 30% more likely to be culled than their less-inbred peers. Furthermore, the impact of inbreeding on survival may rise throughout parities; for example, du Toit et al., 2012 found a greater correlation between inbreeding and survival in second-lactation Jersey cattle in South Africa than in their first-parity counterparts.
Because mature cows who are highly productive and need minimal veterinary treatments are extremely lucrative, genetic increase of lifespan may have a large economic effect on dairy herds (Garca-Ruiz et al., 2016; Dallago et al., 2021). Furthermore, most cows do not recoup their raising expenses until the second lactation (Boulton et al., 2017), and early culling of cows results in economic losses for the farmer. Longevity increases may also have an impact on environmental sustainability and animal welfare. Increased annual herd replacement rates, for example, can contribute to higher greenhouse gas emissions at the farm level (Wall et al., 2012; Grandl et al., 2019), and higher involuntary culling rates in young animals can indicate poor welfare, which can influence consumers’ perceptions of and demand for dairy products. Furthermore, excess heifers that are not required as herd replacements may be sold to generate extra farm revenue (Dallago et al., 2021). Finally, by combining the use of sexed semen on young cows and heifers with the use of beef semen on older cows, farmers can profit from high milk production from mature cows without jeopardising genetic progress, allowing mature cows that are healthy and reproductively sound to remain in the herd for one or two additional lactations.
Management practises, infrastructure, herd size, economic demands, and other variables have all lowered the likelihood of cow survival in commercial dairy herds. For example, with the introduction of sexed sperm, a greater number of heifers are now accessible as herd replacements. Furthermore, producers may be driven to raise culling rates if facilities or available area restrict herd size (de Vries, 2020). Furthermore, genomic selection has accelerated genetic development and produced replacement heifers with increased milk production capacity (Meuwissen et al., 2001; Williams et al., 2022b). Despite genetic advances in productive life and other fitness qualities, these and other variables have resulted in a lower chance of surviving to old ages in Jerseys and other breeds. This apparent paradox results from ongoing changes in the balance of voluntary (economic) and involuntary (forced) culling, and breed improvement programmes should aim to improve animals’ genetic proclivity to remain healthy, fertile, and productive as long as they can make greater economic contributions to the herd than their potential replacements.
Source: Journal of Dairy Science