Agricultural News
OSU's Dr. Glenn Selk says Hot Weather in Late Gestation can Affect Fall Birth Weights
Wed, 03 Aug 2011 14:18:49 CDT
The summer of 2011 will have impacts on the cattle industry in many ways. One of the more subtle results from the extreme July and August heat will be a reduction in birth weights of fall-born calves. Oklahoma State University research (Selk and Buchanan. 1990 OSU Animal Science Research Report, linked below) in the late 1980's and early in the 90's provided information about the reduced birth weight of fall born calves versus spring born calves. According to Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, the average difference was about 4.5 pounds and was similar to the overall difference between heifer and bull calves.
More recently, Oklahoma State University physiologists studied early fall (August) and late fall (October) calving cows. Data from two successive years were combined for 50 Angus X Hereford crossbred cows. The "early" and "late" fall calving cows had been artificially inseminated in early November or early January, respectively. Semen from the same sire was used for all cows. All cows were exposed to a single cleanup bull for 35 days at 4 days after the AI season.
The weather prior to calving was significantly different for late pregnancy in the two groups. The average maximum temperature the week before calving was 93 degrees F. for the "early" fall group. The average maximum temperature the week before parturition in the "late" calving group was 66 degrees F. There was a 100% survival rate for calves in both groups and both groups of cows had very high re-breeding rates (93% and 96%, respectively).
The average birth weight was 3.74 pounds lighter for the calves born to "early" cows as compared to the "late" cows in year 1 of the study. The average birth weight was a whopping 9.68 pounds lighter for the calves from "early" cows in year 2. (Source: Kastner, Wettemann, and co-workers. 2004 OSU Animal Science Research Report, linked below.)
The reason that early fall calving cows have lighter birth weights is generally attributed to the fact that the cows are gestating in hot weather. Blood flow patterns of cattle during periods of high temperatures change in an effort to dissipate heat from the body. Blood (and the nutrients that it carries) is shunted to the outer extremities during hot weather to dissipate heat.
Therefore less blood flow is sent to the inner core of the cow where the fetus is gestating. This subtle change in blood flow is commonly thought to be the reason that lighter birth weights occur to cattle that are in the last trimester of pregnancy in June, July, and August.
Producers with early fall-calving cows should expect lighter (and perhaps weaker) calves that will be born early this fall calving season.
Click here to see the 1990 OSU Animal Science Research Report
Click here to see the 2004 OSU Animal Science Research Report
Our thanks to Dr. Glenn Selk for this latest article- it's a part of the weekly Cow Calf Corner electronic newsletter that Dr. Derrell Peel and Dr. Selk of OSU produce on most Mondays.
WebReadyTM Powered by WireReady® NSI
Top Agricultural News
More Headlines...
