A recent study published in the Canadian Journal of Animal Science sheds light on the question of how this year’s drought might affect next year’s calf crop.
Dr. Cheryl Waldner and Dr. Fabienne Uehlinger from the Western College of Veterinary Medicine at the University of Saskatchewan described a study where blood samples were collected from 899 beef calves that were less than 30 days of age. These calves originated from 150 cow-calf herds in Alberta and Saskatchewan and were sampled in the 2002 calving season.
Many areas of Alberta and Sask-atchewan were under the effects of a significant drought in 2001 and 2002, which has similarities to the current grazing season.
The blood samples were analyzed for serum vitamin A and vitamin E concentrations. Samples were also evaluated for colostrum intake by measuring serum immunoglobulins, which reflect antibodies received when the calf consumes colostrum shortly after birth.
These herds were relatively well-managed as reflected by the relatively low death rates of the calves followed in the study, at about three percent.
Approximately half of the producers surveyed injected their calves with selenium and vitamin E at birth.
Only 11 percent of producers used selenium injections for cows and 22 percent used injectable vitamin A in the cows. Seventeen percent of producers did not report any commercial trace mineral or vitamin supplement used in their cow herds. Only 21 percent of producers surveyed reported supplementing specifically with vitamin A in their cow rations.
Analyzing the vitamin levels in the calf samples revealed that 58.3 percent of the calves had less than adequate levels of vitamin A for their age and 12.9 percent had less than adequate levels of vitamin E.
The authors were able to use treatment records and mortality records to demonstrate that calves with low serum vitamin A (the lowest 25 percent) were 2.8 times more likely to die. Calves with low serum vitamin E were 3.2 times more likely to be treated for scours.
The relationship of vitamin A levels to drought conditions is well-established and is demonstrated in this study once again. Vitamin A levels were significantly lower in herds that were in geographical areas that had less than 200 millimetres of rain in the previous growing season when compared to herds that received adequate precipitation.
Vitamin E levels were not affected by the levels of precipitation in this study.
Vitamin A is manufactured by cattle from a precursor found in plants known as beta-carotene. Plants that are green and growing are rich in beta-carotene, while concentrates or plants that are growing in drought conditions are usually not a good source of vitamin A and beta-carotene.
Other studies have shown that cattle that are grazing green plants during summer tend to have higher vitamin A levels than cattle being fed stored forages in the winter. The precursor to vitamin A degrades over time with harvesting, dehydration, and storage of forages and up to 50 percent of beta-carotene may be lost over time.
Newborn calves get almost all of their vitamin A from the colostrum they consume shortly after birth. They are born with very low levels of vitamin A and are reliant on their dam’s vitamin A levels in her colostrum. If a cow has been grazing under drought conditions or fed stored feeds low in vitamin A, the calf will be at a much higher risk of being deficient in vitamin A, which is necessary for adequate immune function and normal growth.
This study demonstrated that the calves deficient in vitamin A were almost three times more likely to die than calves that have adequate levels of vitamin A for their age.
The study was also able to show that calves from heifers were also more likely to be deficient in vitamin A or vitamin E when compared to calves born to cows. This might be due to the fact that calves from heifers were less likely to consume adequate colostrum because of poorer mothering ability or a higher risk of calving difficulty. It is also a common finding that any nutritional problem will probably have a greater impact on heifers because they are still growing and have higher nutritional demands.
The effects of drought on the quality of grazed forages and stored forages in terms of vitamin A levels was particularly noteworthy.
The authors conclude that producers should consider supplementing cows and particularly heifers, especially in years where there is significant drought.
Many cow-calf producers in Western Canada are experiencing significant levels of drought this year and may be low in beta-carotene and vitamin A. Consult a veterinarian or nutritionist about options for supplementing cows and also next year’s calves with vitamin A and E.
John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.