Effect of Heat Stress on Nonreturn Rate in Holsteins: Fixed-Model Analyses

Abstract

The objective of this study was to examine the relationship between reproductive traits and heat stress. Nonreturn rate at 45 d (NR45) was analyzed in a fixed-effect model that included the temperature-humidity index (THI) from a nearby weather station as a measurement of heat stress. Data consisted of 150,200 first inseminations at first and later parities of 110,860 Holstein cows from 550 herds in Georgia, Tennessee, and Florida with weather information from 16 weather stations. THI on the day of the insemination, 2 d prior, 5 d prior, 5, 10, 20, and 30 d after insemination were studied as independent variables. The THI on the day of insemination showed the highest effect on NR45, followed by 2 d prior, 5 d prior, and 5 d after insemination, but no relationship was found with THI at 10, 20, and 30 d after insemination. NR45 showed a decrease of 0.005 per unit increase in THI on the day of insemination for THI >68. First and later parities presented similar thresholds but responded differently to an increase in THI, with NR45 being significantly lower and more susceptible to increases of THI in cows in their first parity than in later parities (0.008 vs. 0.005 decrease). Threshold for sensitivity to heat stress changed with the states, with Florida, Georgia, and Tennessee having thresholds of 70, 70, and 66, respectively. The decrease in NR45 per unit increase of THI was 0.007, 0.005, and 0.006 for Florida, Georgia, and Tennessee, respectively. With respect to only the Florida data, the final fixed-effect model used was NR45 = herd(year) + month(year) + month(year) + age(parity) + days in milk + 100d milk + THI + error. Animals with more than 150 d in milk (DIM) had a 0.16 lower NR45 than animals with less than 60 DIM at insemination. Lower milk-producing animals showed 0.08 higher NR45 than higher-producing animals. A difference of 0.10 in NR45 was observed between THI lower than 70 and THI 84. This variation in NR45 caused by THI changes is sufficient to merit further studies to examine genetic components of heat tolerance for this trait.

Adaptation to climate change – exploring the potential of locally adapted breeds

“…Most selection relevant to climate adaptation is undertaken in developed countries with commercial breeds, most of which are of temperate origin. Considerable genetic variance caused by heat stress was related to high daily THI in Jersey and Holstein Friesian dairy cattle (Ravagnolo and Misztal, 2002;Hayes et al, 2009). Therefore, selection for heat tolerance in highoutput breeds based on rectal temperature measurements and inclusion of a THI in genetic evaluation models is promising.…”

Future consequences and challenges for dairy cow production systems arising from climate change in Central Europe – a review

“…Hansen (2007) postulated that identification of the genes that are responsible for heat tolerance in cattle could diminish the risk of embryonic mortality, which is currently the leading cause of fertility problems in high yielding dairy cows (Diskin and Morris, 2008). Data comparing non-return rates at day 45 after artificial insemination (AI) in Holstein/Friesian cows in different states of the United States showed that resistance to heat stress varies possibly because of a genetic variability in heat tolerance within the breed (Ravagnolo and Misztal, 2002). Unravelling the underlying mechanisms by which heat stress impairs male fertility may help to alleviate the effects on sperm quality and subsequent embryo development.…”

Defining and evaluating heat stress thresholds in different dairy cow production systems

“…Many studies from so called 'hot weather areas' in the world found a decline in milk production and a depression of reproductive performance in dairy cows due to heat stress (e.g. Ravagnolo & Misztal 2002, Bohmanova et al 2007.…”