Influence of heat stress on reproductive performance in dairy cows and opportunities to reduce its effects – a review

T. Penev1*, D. Dimov1, N. Vasilev2, J. Mitev1, Tch. Miteva1, I. Marinov3, M. Stojnov1

1Department of Applied Ecology and Animal Hygiene, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria
2Department of Obstetrics, reproduction and reproductive disorders, Faculty of Veterinary Medicine, Trakia University, 6000 Stara Zagora, Bulgaria
3Department of Animal Husbandry – Ruminants and Dairy Farming, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria

(Manuscript received 14 September 2020; accepted for publication 2 March 2021)

Abstract. The goal of this review is to consider and discuss the scientific literature related to the effect of heat stress (HS) on reproductive performance in dairy cows and opportunities to reduce its effects. The information in literature shows that the HS topic in dairy cows began to be discussed in the 1970s. As genetic progress related to productivity increases, the requirements for cows also increase, including for their reproduction performance. In the present review, a significant array of scientific papers is examined, as a result of which it is established that HS has a multifaceted effect on reproduction in dairy cows. The main role for the negative impact of HS is the effect of high ambient temperature on the hypothalamic-pituitary-ovarian axis. As a result, hormonal changes occur in the body of cows, which affect the behavior of cows in estrus, the development of follicles in the ovaries and the survival of the embryo in the uterus. These changes affect the main elements of cattle breeding such as length of days open interval, conception rate, number of inseminations required for conception. To mitigate the negative impact of HS on cows, methods have been developed for better estrus detection, for microclimate control, as well as for hormonal treatment of cows in order to increase reproductive performance. Although some progress has been made in each of the measures, HS still poses a serious reproductive problem for dairy cows, especially in the countries with warmer climates. This provokes the interest of many scientists around the world who seek to offer a solution/mitigation to this problem.

Effect of herd and number of lactation on milking temperament score in Black-and-White cows

Abstract. The study comprises 143 Black-and-White cows from three cattle farms with free cubicle rearing (one) and tied rearing (two). The number of cows by farms is as follows: farm 1 – 69 cows, farm 2 – 34 cows and farm 3 – 40 cows. All cows in lactation from Ist to VIIth at the time of evaluation have been included, respectively in Ist lactation – 40 cows, in IInd – 28 and in IIIrd and further lactation – 75 cows. To assess the temperament a 5-point scale has been used, respectively 1 – very nervous and 5 – very calm cows. Recording the milking temperament has been done once during lactation and all cows currently in lactation on the three farms have been assessed. Primiparous up to the 30th day after calving have not been included in the assessment. Statistically significant effect of the farm on the milking temperament score has not been reported. In the three studied farms relatively high, above 80% share of calm cows has been reported – scores from 3 to 5. The highest is the relative share of nervous animals (scores 1 and 2) of farm 2 – 17.6%, and the lowest – of farm 3 – 12.5%. Statistically significant effect of the number of lactation on the milking temperament score has been reported. The highest is the percentage of nervous animals – 22.5% in cows at first lactation and, respectively, the lowest is the share of the calm ones – 77.5%. With cows after Ist lactation the percentage of nervous cows is half less and it remains almost unchanged in later lactations. The highest is the LS-mean score for the temperament of cows in IIIrd and further lactations – 4.15, followed by those in IInd. The lowest is the LS-mean score for temperament of cows in first lactation – 3.82.

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Comparative investigation on some welfare indicators of cattle under different housing systems

J. Mitev, T. Penev, Zh. Gergovska, Ch. Miteva, N. Vassilev, K. Uzunova

Abstract. Dairy cattle welfare is of exceptional importance in modern production systems. The purpose of the present study was to compare the effect of some of most popular contemporary solutions for free-stall housing of dairy cows on some welfare indicators. It was performed with 150 Holstein-Friesian cows in three farms as followed: housed freely in group boxes in a semi-open barn (farm A), and housed freely in group stalls, with individual cubicles of a different size (farms B and C). The results showed that the free housing in groups with straw bedding was optimal with regard to the prevalence of traumatism as seen from the least percentage of body decubitus ulcers – 2% of cows, but it was most unfavorable from the point of view of body hygiene level. The free housing in individual cubicles (farms B and C) with the specific cubicle and neck rail dimensions were a prerequisite for increased trauma incidence and were not compliant with the allowances of this welfare indicator. The application of systems for complex evaluation of the level of dairy cattle welfare allows for an easy detection of existing flaws and disadvantages at a specific farm and for timely suggestion of efficient measures for their correction.

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