Genetic analyses of protein yield in dairy cows applying random regression models with time-dependent and temperature x humidity-dependent covariates

Tropical and sub-tropical climates are characterized by high temperature and humidity, during at least part of the year. Consequently, heat stress is common in Holstein cattle and productive and reproductive losses are frequent. Our objectives were as follows: (1) to quantify losses in production and quality of milk due to heat stress; (2) to estimate genetic correlations within and between milk yield (MY) and milk quality traits; and (3) to evaluate the trends of genetic components of tolerance to heat stress in multiple lactations of Brazilian Holstein cows. Thus, nine analyses using two-trait random regression animal models were carried out to estimate variance components and genetic parameters over temperature-humidity index (THI) values for MY and milk quality traits (three lactations: MY × fat percentage (F%), MY × protein percentage (P%) and MY × somatic cell score (SCS)) of Brazilian Holstein cattle. It was demonstrated that the effects of heat stress can be harmful for traits related to milk production and milk quality of Holstein cattle even though most herds were maintained in a modified environment, for example, with fans and sprinklers. For MY, the effect of heat stress was more detrimental in advanced lactations (−0.22 to −0.52 kg/day per increase of 1 THI unit). In general, the mean heritability estimates were higher for lower THI values and longer days in milk for all traits. In contrast, the heritability estimates for SCS increased with increasing THI values in the second and third lactation. For each trait studied, lower genetic correlations (different from unity) were observed between opposite extremes of THI (THI 47 v. THI 80) and in advanced lactations. The genetic correlations between MY and milk quality trait varied across the THI scale and lactations. The genotype × environment interaction due to heat stress was more important for MY and SCS, particularly in advanced lactations, and can affect the genetic relationship between MY and milk quality traits. Selection for higher MY, F% or P% may result in a poor response of the animals to heat stress, as a genetic antagonism was observed between the general production level and specific ability to respond to heat stress for these traits. Genetic trends confirm the adverse responses in the genetic components of heat stress over the years for milk production and quality. Consequently, the selection of Holstein cattle raised in modified environments in both tropical and sub-tropical regions should take into consideration the genetic variation in heat stress.

Section: Discussionsupporting

confidence: 70%

Section: Discussionsupporting

confidence: 56%

Section: Datamentioning

confidence: 99%

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Genetics of heat tolerance for milk yield and quality in Holsteins

Júnior

Bignardi

Pereira

et al. 2017

“…While the effects of heat stress on dairy cows has been well-documented in tropical and subtropical regions (e.g. West et al, 2003;Dikmen and Hansen, 2009), a growing number of studies has also reported associations between THI and milk traits in temperate regions where tolerance to heat stress is lower (Bruegemann et al, 2011;Hammami et al, 2013;Dunn et al, 2014). Moreover, temperatures are predicted to increase over the 21st century in southern Scotland, especially in summer, with an expected mean daily maximum temperature increase of 4.3°C by the 2080s with a very slight reduction (0% to 5%) in humidity (Jenkins et al, 2009).…”

mentioning

confidence: 99%

Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management

Hill

Wall

2015

113

A better understanding of how livestock respond to weather is essential to enable farming to adapt to a changing climate. Climate change is mainly expected to impact dairy cattle through heat stress and an increase in the frequency of extreme weather events. We investigated the effects of weather on milk yield and composition (fat and protein content) in an experimental dairy herd in Scotland over 21 years. Holstein Friesian cows were either housed indoors in winter and grazed over the summer or were continuously housed. Milk yield was measured daily, resulting in 762 786 test day records from 1369 individuals, and fat and protein percentage were sampled once a week, giving 89 331 records from 1220 cows/trait. The relative influence of 11 weather elements, measured from local outdoor weather stations, and two indices of temperature and humidity (THI), indicators of heat stress, were compared using separate maximum likelihood models for each element or index. Models containing a direct measure of temperature (dry bulb, wet bulb, grass or soil temperature) or a THI provided the best fits to milk yield and fat data; wind speed and the number of hours of sunshine were most important in explaining protein content. Weather elements summarised across a week's timescale from the test day usually explained milk yield and fat content better than shorter-scale (3 day, test day, test day −1) metrics. Then, examining a subset of key weather variables using restricted maximum likelihood, we found that THI, wind speed and the number of hours of sunshine influenced milk yield and composition. The shape and magnitude of these effects depended on whether animals were inside or outside on the test day. The milk yield of cows outdoors was lower at the extremes of THI than at average values, and the highest yields were obtained when THI, recorded at 0900 h, was 55 units. Cows indoors decreased milk yield as THI increased. Fat content was lower at higher THIs than at intermediate THIs in both environments. Protein content decreased as THI increased in animals kept indoors and outdoors, and the rate of decrease was greater when animals were outside than when they were inside. Moderate wind speeds appeared to alleviate heat stress. These results show that milk yield and composition are impacted at the upper extreme of THI under conditions currently experienced in Scotland, where animals have so far experienced little pressure to adapt to heat stress.Keywords: climate change, fat percentage, heat stress, protein percentage, THI ImplicationsClimate change is expected to bring about drier, hotter summers and an increased frequency of extreme weather events across Europe. Here we show that milk yield and quality decline at the upper extremes of temperature and humidity even under conditions currently experienced in Scotland. We identify the values of temperature and humidity, and of other weather elements, at which performance begins to decrease. These estimates could be used in conjunction with climate projections to help policy makers un...

“…These validation studies were carried out primarily in (sub) tropical and arid regions, and they were carried out on lessproductive dairy cows rather than those generally reared nowadays (Zimbelman et al, 2009), especially in temperate regions. On the other hand, Brügemann et al (2011) identified a lower daily average THI value of 60 as the threshold for declining milk protein content in German Holstein cows. Hammami et al (2013) proposed a daily average THI value of 62 as a new threshold for Western European Holstein cows, above which milk yield was found to decline with 0.164 kg/ day per cow.…”

Section: Introductionmentioning

confidence: 99%

Effect of summer conditions and shade on the production and metabolism of Holstein dairy cows on pasture in temperate climate

laer¹,

Tuyttens

Ampe³

et al. 2015

For dairy cattle on pasture in temperate regions, it is largely unknown to what degree hot summer conditions impact energy metabolism, milk yield and milk composition and how effective shade is in reducing these negative effects. During the summer of 2012, a herd of Holstein cows was kept on pasture without access to shade (treatment NS). During the summers of 2011 and 2013, the herd was divided into a group with (treatment S) and a group without (treatment NS) access to shade. Shade was provided by young trees combined with shade cloths (80% reduction in solar radiation). A weather station registered the local climatic conditions on open pasture, from which we calculated daily average Heat Load Index (HLI) values. The effects of HLI and shade on rectal temperature (RT), blood plasma indicators of hyperventilation and metabolic changes due to heat stress, milk yield and milk composition were investigated. RT increased with increasing HLI, but was less for S cows than for NS cows (by 0.02°C and 0.03°C increase per unit increase of HLI, respectively). Hyperchloraemia (an increased blood plasma concentration of Cl − ), a sign of hyperventilation, increased for NS cows but not for S cows. The plasma concentration of alkaline phosphatase, a regulator of energy metabolism in the liver, decreased with increasing HLI for NS cows only. Access to shade, thus, reduced the effect of HLI on RT, hyperchloraemia and the regulation of metabolism by the liver. As HLI increased, the plasma concentration of cholesterol decreased (indicating increased lipolysis) and the plasma concentration of creatinine increased (indicating increased protein catabolism). These effects did not differ between S and NS cows. For NS cows, after a lag-time of 2 days, the milk yield decreased with increasing HLI. For S cows, the milk yield was unaffected by HLI and its quadratic factor. The milk concentrations of lactose, protein and fat decreased as HLI increased, but only the effect on milk protein content was remediated by shade. In conclusion, access to shade tempered the negative effects of high HLI on RT, hyperchloraemia and a blood plasma indicator of changing energy metabolism (generally) as well as prevented the decrease in milk yield observed in cows without access to shade.Keywords: heat stress, dairy cattle, temperate climate, milk, metabolism ImplicationsFor dairy cattle on pasture in temperate regions, it is largely unknown to what degree hot summer conditions impact energy metabolism, milk yield and milk composition and how effective shade is in preventing this. In this study, the effect of Belgian summer weather on dairy cows with and without access to shade was investigated. Hot summer conditions affected body temperature, metabolism and milk yield and composition. Some effects (the increase in body temperature and the decrease in milk yield, among others) were reduced by access to shade, provided by trees combined with shade cloth.