Notes from the Joint American Dairy Science and Animal Science Association Meetings

Dr. Allen Young
USU Extension Dairy Specialist

I just got back from the annual Dairy and Animal Science meetings held in Phoenix, Arizona. Besides the Arizona summer heat, there were some topics and ideas at this forum that I thought were pretty hot, too. While I will probably report about these more extensively in the future, I wanted to at least mention a couple of things right away that I felt were interesting.

The first has to do with the ideas about altering photoperiod in dry cows to enhance production in the next lactation. You are probably aware that increasing the length of daylight in the winter can increase milk production in lactating cows. However, the research coming out now shows that SHORT day photoperiods are what works in dry cows, not long days. Work from the University of Illinois and University of Vermont showed that short day photoperiod during the dry period leads to increased milk production in the subsequent lactation. In addition, dry matter intake was increased during the dry period. The most interesting finding was that the function of immune cells in the cow was enhanced by short day photoperiod and this effect persisted at least through two days postcalving. How we can manipulate the photoperiod of dry cows and lactating cows in opposite directions under our management systems here in the West remains to be seen; however, the results are strong enough for me that I think it is definitely worth trying.

The second piece of research that I want to mention is from the University of Wisconsin, Madison. Milo Wiltbank and Hernando Lopez (a former USU graduate student) have been looking at the relationship between level of milk production and estrus behavior in lactating dairy cows. A total of 267 cows were fitted with the Heat Watch system to measure mounting behavior and were checked for ovulation weekly using ultrasound. Cows were divided into two groups, those that were producing over 87 lb milk per day and those producing less than 87 lbs. High producing cows showed reduced duration and intensity of estrus compared with the lower producers. The probability of detecting estrus in high producing cows was inversely related to the level of milk production. In other words, as milk production went up, the probability of detecting estrus in the high producers went down. In addition, because of the shorter duration of estrus and fewer mounts, the probability of detecting a cow in heat was also inversely proportional to the amount of time spent in heat detection. For example, with a cow producing 66 lb milk per day and detected for heat every 6 hrs, the probability of catching the cow in heat would be approximately 92%. If the heat detection was done every 12 hours, for the same level of production the probability would be reduced to 76%. If you were only checking for heat every 24 hrs, the probability would be 52%. Now if you raise the level of milk production to 110 lb per day, the probability of detecting heat at 6, 12, and 24 hr intervals would be 49%, 32%, and 12%, respectively. Managers of higher producing herds need to increase the amount of time they spend on heat detection or go to some type of reproductive program that allows them to predict when cows are going to ovulate.

Finally (for this article), researchers from Purdue University looked at the behavior of cows and heifers during transition by use of video cameras. Resting prior to calving was highly correlated with increased milk production postcalving. Also, maximizing dry matter intake during the dry period increased the dry matter intake and milk production during lactation. This just reinforces the idea of actively managing dry cows to maximize comfort and intake. Finally, the behavior differences in time spent feeding relative to calving for heifers was different than for cows, suggesting that there may be some benefit to keeping heifers separate from cows during the transition period. This remains to be seen, but it is definitely food for thought.

If you have any questions about any of the above highlighted research projects, feel free to contact me.