Seasonality of fertility measured by physical activity traits in Holstein cows

Abstract

Seasonality of female fertility traits, including the interval from calving to first high activity (CFHA), duration of high activity episode (DHA), and strength of high activity episode (SHA) of first estrus, were studied. The physical activity traits were derived from electronic activity tags for 20,794 Holstein cows in 135 commercial Holstein herds in Denmark. Data were categorized in 3 ways: (1) into 4 seasons of calving: winter (January-March), spring (April-June), summer (July-September), and fall (October-December); (2) into 2 seasons: a cold season (October-March) and a warm season (April-September); and (3) into an increasing light season (IL; January-June), where daylight hours gradually increased, and a decreasing light season (DL; July-December), where daylight hours gradually decreased. At the phenotypic level, least squares means of CFHA were highest at 55d for cows calving in December and lowest at 31d for cows calving in September. The highest least squares means of DHA and SHA were recorded for cows calving in November and lowest for cows calving in May and June. Genetic parameters for all traits were estimated using average information-REML in a bivariate animal model that treated the same trait in different calving seasons as different traits. Heritability estimates for CFHA were highest for the winter season (0.13) and low for the other seasons (0.03-0.04), whereas heritability estimates for DHA and SHA were lowest for winter and highest for fall. Heritability estimates for CFHA for the cold season (0.17) was higher than that for the warm season (0.10). Heritability estimates of CFHA for the IL season (0.12) was higher than for the DL season (0.07), but the opposite pattern was found for DHA and SHA. Genetic correlations (rA) of CFHA between winter and summer (rA=0.34 ± 0.27), and winter and fall (rA=0.65 ± 0.20) were significantly lower than unity. The corresponding correlations of DHA and SHA between seasons were all close to unity, except for the correlation of SHA between winter and fall (rA=0.36 ± 0.34). When the year was split into only 2 seasons, the genetic correlation of CFHA between cold and warm seasons was only moderate (rA=0.46 ± 0.15) but was slightly stronger between IL and DL seasons (rA=0.63 ± 0.16); both significantly deviated from unity. These results indicate the existence of a genotype by environment interaction for CFHA regardless of calving season classification.

Genotype by environment interaction for the interval from calving to first insemination with regard to calving month and geographic location in Holstein cows in Denmark and Sweden

“…Oseni et al (2004) and Ravagnolo and Misztal (2002), who observed low heritability estimates of nonreturn rate when the heat stress level were high using temperature humidity index as a continuous environmental descriptor in the reaction norm model in US Holsteins. Our results were in agreement with those of Ismael et al (2016), who found that heritability of the interval from calving to first high activity (measured from activity tags) for winter calvings was 3 times higher than the heritability for spring and summer calvings Heritability and genetic variance of CFI across different geographic locations were not constant. Heritability estimates decreased with increasing latitude, from LOC-2 to LOC-8, where the heritability estimate obtained for LOC-2 (the highest) was twice the heritability estimate found for LOC-8 (the lowest).…”

“…Another possible explanation relates to the directionality of the environmental gradients; that is, whether daylight length and temperature are increasing (January to June) or decreasing (July to December). Such an effect was reported by Ismael et al (2016) on calving to first high activity, who observed that cows calving during the increasing daylight season (January to June) had their first high-activity episode an average of 8 d later than cows calving during the decreasing daylight season (July to December).…”

“…A similar effect of calving season was found in the ability of cows to return to cyclic estrus after calving by progesterone profiling (Petersson et al, 2007). Another example is the effect of calving season on the interval from calving to first high activity measured by activity tags, where summer calvers had their first high-activity episode 12 d earlier than spring calvers (Ismael et al, 2016). The trait was also found to be highly correlated with CFI (genetic correlation = 0.96; Ismael et al, 2015).…”

“…In that same study, those authors found a genetic correlation of 0.67 between the regular and heat stress effect due to months of calving using random regression of days open on the fixed solution of days open in different calving months. Furthermore, our research group found that the genetic correlation between warm and cold calving months for the interval from calving to first estrus was significantly less than unity (r a = 0.46; Ismael et al, 2016).…”

Milk progesterone measures to improve genomic selection for fertility in dairy cows

“…Studies of physical activity derived traits e.g., the interval from calving to the first sign of high activity (CFHA) have reported higher heritability, ranging from 0.12 to 0.18 (Løvendahl and Chagunda, 2009;Ismael et al, 2015). Though CFHA has been suggested as a measure for resumption of ovarian activity, Ismael et al, (2016) showed that a drawback is that activity monitor derived fertility traits are seasonally sensitive.…”