Genetic parameters of milk production traits in response to a short once-daily milking period in crossbred Holstein × Normande dairy cows

Abstract

Despite its potential utility for predicting cows' milk yield responses to once-daily milking (ODM), the genetic basis of cow milk trait responses to ODM has been scarcely if ever described in the literature, especially for short ODM periods. This study set out to (1) estimate the genetic determinism of milk yield and composition during a 3-wk ODM period, (2) estimate the genetic determinism of milk yield responses (i.e., milk yield loss upon switching cows to ODM and milk yield recovery upon switching them back to twice-daily milking; TDM), and (3) seek predictors of milk yield responses to ODM, in particular using the first day of ODM. Our trial used 430 crossbred Holstein × Normande cows and comprised 3 successive periods: 1 wk of TDM (control), 3 wk of ODM, and 2 wk of TDM. Implementing ODM for 3 wk reduced milk yield by 27.5% on average, and after resuming TDM cows recovered on average 57% of the milk lost. Heritability estimates in the TDM control period and 3-wk ODM period were, respectively, 0.41 and 0.35 for milk yield, 0.66 and 0.61 for milk fat content, 0.60 and 0.80 for milk protein content, 0.66 and 0.36 for milk lactose content, and 0.20 and 0.15 for milk somatic cell score content. Milk yield and composition during 3-wk ODM and TDM periods were genetically close (within-trait genetic correlations between experimental periods all exceeding 0.80) but were genetically closer within the same milking frequency. Heritabilities of milk yield loss observed upon switching cows to ODM (0.39 and 0.34 for milk yield loss in kg/d and %, respectively) were moderate and similar to milk yield heritabilities. Milk yield recovery (kg/d) upon resuming TDM was a trait of high heritability (0.63). Because they are easy to measure, TDM milk yield and composition and milk yield responses on the first day of ODM were investigated as predictors of milk yield responses to a 3-wk ODM to easily detect animals that are well adapted to ODM. Twice-daily milking milk yield and composition were found to be partly genetically correlated with milk yield responses but not closely enough for practical application. With genetic correlations of 0.98 and 0.96 with 3-wk ODM milk yield losses (in kg/d and %, respectively), milk yield losses on the first day of ODM proved to be more accurate in predicting milk yield responses on longer term ODM than TDM milk yield.

Bovine Teat Cistern Microbiota Composition and Richness Are Associated With the Immune and Microbial Responses During Transition to Once-Daily Milking

“…With about two third of the 93 initially non-inflamed and noninfected quarters displaying early inflammation at day 3 (D3) (within G1, G4, and G5 groups), the inflammatory response was likely related to the transition to ODM rather than any other external event, although we cannot totally exclude it. This is also in agreement with previous studies reporting at least a transient udder inflammation following transition to ODM (Stelwagen et al, 2013;Charton et al, 2018).…”

“…All experiments were performed in accordance with relevant guidelines and regulations. Crossbred Prim'Holstein x Normande cows were kept indoors in deep litter housing with daily mulching and fed as previously described (Charton et al, 2018). Cows were milked twice daily at 06h45 and at 16h45 and, after the switch to ODM at D0, they were milked once daily at 7h45 for 3 weeks.…”

“…This hypothesis is supported by the correlation observed between the initial teat microbiota richness (et D0) and IL-8 secretion in milk following transition to ODM (at D3). Transition to ODM through an increase in the milking interval changes the residence time of bacteria in the teat and leads to modifications of milk composition (Charton et al, 2018) that can affect the growth capacities and competition for nutrients between microbiota members. A more diverse microbiota (in C2 compared to C1 quarters) would be more sensitive to such changes in environmental conditions, at least because more OTUs are likely to be affected.…”

“…Changes in milking frequency can indeed be seen as a perturbation of mammary gland homeostasis. ODM results in milk accumulation and stasis in the mammary gland for 24 h, and has been associated with, at least transiently, udder inflammation associated or not with an infection (Stelwagen et al, 2013;Charton et al, 2018). An increase in SCC was indeed previously reported during transition from TDM to ODM (Rémond and Pomiès, 2007;Stelwagen et al, 2013;Charton et al, 2018).…”

“…ODM results in milk accumulation and stasis in the mammary gland for 24 h, and has been associated with, at least transiently, udder inflammation associated or not with an infection (Stelwagen et al, 2013;Charton et al, 2018). An increase in SCC was indeed previously reported during transition from TDM to ODM (Rémond and Pomiès, 2007;Stelwagen et al, 2013;Charton et al, 2018). In our study, quarters initially free of inflammation and infection (i.e., no mastitis) were classified based on both their inflammatory response (SCC and Interleukin-8 in milk) and the development of infection following transition to ODM.…”