Technical note: Accelerometer-based recording of heavy breathing in lactating and dry cows as an automated measure of heat load.

Monitoring thermal status using a reliable, practical method is essential for proper cattle management during periods of high heat load. Our objective was to determine whether accelerometer-based tags, which measure heavy breathing and other behaviors on a minute-by-minute basis, accurately reflect thermal status. We hypothesized that the tags would mirror core body temperature as recorded by continuous intravaginal loggers, and that response to a cooling intervention would also be captured. Data were collected during a 3-d period from 10 late dry and 20 high-producing cows at peak lactation, each fitted with an intravaginal temperature logger and tag attached to a collar. The relationship between vaginal temperature and proportion of cows recorded as breathing heavily averaged over the three 24-h periods was described separately for each group, and during a 1-h block capturing 2 intensive cooling sessions in lactating cows. Finally, the log of the odds of a cow breathing heavily in each minute relative to vaginal temperature in cows before cooling was analyzed using a linear mixed model. The proportion of cows breathing heavily in a group mirrors changes in vaginal temperature in both dry and lactating cows. In contrast to the dry cows, lactating cows suffered from excessive heat load to a much greater degree. Cooling intensively with showers and fans effectively mitigates the effects of excessive heat load, as reflected by response in vaginal temperature and proportion of cows breathing heavily. The probability of heavy breathing increases by approximately 10% for each 0.5°C rise in vaginal temperature above 39.0°C. In conclusion, accelerometer-based technology that automatically records heavy breathing provides a practical means of continuously assessing heat load status of dairy cows, whether lactating or dry, and their response to cooling intervention. This has the potential to optimize both cow and resource management during periods of high heat load.

Seasonal and parity effects on ghrelin levels throughout the estrous cycle in dairy cows.

In dairy cows, heat stress depresses appetite, leading to decreased food intake, a negative energy balance, and modifies ghrelin levels. Ghrelin is a gut-brain peptide with two major forms: acylated, with an O-n-octanoylated serine in position 3, and nonacylated. To date, the effect of heat stress and estrous cycle on ghrelin secretion in dairy cows has not been studied. We characterized ghrelin secretion during the estrous cycle in each, the winter and the summer seasons. We further examined the effects of parity on ghrelin secretion. Blood was collected from 10 primiparous or multiparous Israeli-Holstein dairy cows throughout the estrous cycle, in both, the hot and cold seasons. The levels of acylated and total ghrelin were measured in the blood samples. We found that both acylated and total ghrelin levels during heat stress were lower than their respective levels in the winter in both, primiparous and multiparous cows. No differences in acylated and total ghrelin levels were found between primiparous and multiparous cows in both seasons. We further found that in multiparous but not primiparous cows acylated ghrelin secretion oscillated during the estrous cycle in both seasons. Its levels peaked on the last days of the first follicular wave and on the days before and during ovulation. Interestingly, we found that elevated acylated ghrelin levels correlated with conception success and increased total ghrelin levels were associated with successful conception from first insemination. Our data is the first to demonstrate seasonal variation in ghrelin secretion. This study provides evidence for the yet unfamiliar link between heat stress, ghrelin and fertility. Increased circulating acylated ghrelin may contribute to improved fertility in dairy cows. It further raises the possibility of a link between ghrelin levels and successful inseminations. Further research is required to determine the effects of ghrelin on dairy cow performance.

The effect of cooling management on blood flow to the dominant follicle and estrous cycle length at heat stress.

The use of ultrasound imaging for the examination of reproductive organs has contributed substantially to the fertility management of dairy cows around the world. This method has many advantages such as noninvasiveness and immediate availability of information. Adding Doppler index to the ultrasound imaging examination, improved the estimation of blood volume and flow rate to the ovaries in general and to the dominant follicle in particular. The aim of this study was to examine changes in the blood flow to the dominant follicle and compare them to the follicular development throughout the cycle. We further set out to examine the effects of different types of cooling management during the summer on the changes in blood flow to the dominant follicle. For this purpose, 24 Israeli-Holstein dairy cows, under heat stress, were randomly assigned one of two groups: one was exposed to five cooling sessions per day (5CS) and the other to eight cooling sessions per day (8CS). Blood flow to the dominant follicle was measured daily using Doppler index throughout the estrous cycle. No differences in the preovulatory dominant follicle diameter were detected between the two cooling management regimens during the cycle. However, the length of the first follicular wave was significantly longer, whereas the second follicular wave was nonsignificantly shorter in the 5CS group as compared to the 8CS group. In addition, no difference in blood flow was found during the first 18 days of the cycle between the two groups. However, from Day 20 until ovulation a higher rate of blood flow was measured in the ovaries of cows cooled 8 times per day as compared to the 5CS group. No differences in progesterone levels were noted. Finally, the estrous cycle length was shorter in the 8CS group as compared to the 5CS group. Our data suggest that blood flow to the dominant follicle and estrous cycle length is affected by heat stress. Using the appropriate cooling management during heat stress can enhance the blood flow to the ovary and may contribute to improved fertility in dairy cows.

Follicular dynamics and concentrations of steroids and gonadotropins in lactating cows and nulliparous heifers.

Differences in follicular development and circulating hormone concentrations, between lactating cows and nulliparous heifers, that may relate to differences in fertility between the groups, were examined. Multiparous, cyclic, lactating Holstein cows (n=19) and cyclic heifers (n=20) were examined in the winter, during one estrous cycle. The examinations included ultrasound monitoring and daily blood sampling. Distributions of two-wave and three-wave cycles were similar in the two groups: 79 and 21% in cows, 70 and 30% in heifers, respectively. Cycle lengths were shorter by 2.6 days in heifers than in cows, and in two-wave than in three-wave cycles. The ovulatory follicle was smaller in heifers than in cows (13.0+/-0.3 mm versus 16.5+/-0.05 mm). The greater numbers of large follicles in cows than in heifers corresponded well to the higher concentrations of FSH in cows. The duration of dominance of the ovulatory follicle tended to be longer in cows than in heifers. Estradiol concentrations around estrus and the preovulatory LH surge were higher in heifers than in cows (20 versus 9 ng/ml). Progesterone concentrations were higher in heifers than in cows from Day 3 to Day 16 of the cycle. Circulating progesterone did not differ between two-wave and three-wave cycles. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of steroids and gonadotropins; these may account for the differences in fertility between nulliparous heifers and multiparous lactating cows.