Many cows came home in 2017 from pastures parched by drought for much of the grazing season. Without proper supplementation of brood cows through the rest of their gestation, vitamin and mineral deficiencies will show up as health issues next spring with economic consequences that often persist for several more.
It is well established that proper cow nutrition affects calf performance, health and survivability more than any other management factor. When cows are not properly supplemented, problems are magnified in heifers. Now is the time to test forages and grain for nutrient content and work with your veterinarian and other animal health professionals in designing rations for winter.
The interrelationship of vitamin and mineral metabolism by cattle is complicated and subject to year-to-year variations in weather, forage quality, water quality and body condition. Certain nutrients are required by beef cattle in the daily ration, whereas others can be stored in the body. When body stores of a nutrient are high, an example being vitamin A, dietary supplementation is unnecessary until stores are depleted. However, it’s difficult to determine when body stores approach critical levels until signs of deficiency start to appear, which not uncommonly shows up at calving.
At least 17 minerals and five vitamins are required by beef cattle. Minerals are divided into two groups: macro-minerals (calcium, phosphorus, potassium, magnesium and salt or sodium chloride), and trace minerals (copper, selenium, iodine, zinc, cobalt, iron, molybdenum). In a nutrient requirement table, macro-mineral requirements are expressed as per cent in a ration on a dry matter (DM) basis, while trace or micro-mineral needs are expressed in parts per million (ppm) or mg/kg. Trace minerals are often in short supply within the base diet and only small amounts are transferred to nursing calves. Calves rely on liver stores present at birth. Liver stores are replenished when calves begin to ingest forage and supplements. Calf liver stores at birth are linked to liver concentrations in the dam.
Vitamins, like minerals, are essential nutrients for cattle. As a group, they are involved in all aspects of the animal’s metabolism including growth, reproduction and health. There are two general classes of vitamins: water-soluble and fat-soluble. The water-soluble vitamins include vitamin B and vitamin C; fat-soluble vitamins include A, D, E and K.
While all vitamins are essential, vitamins A, D, and E are most relevant from a ration management perspective. In most situations, rumen bacteria supply adequate levels of B vitamins and vitamin K. Exceptions include thiamine deficiencies (polio) and sweet clover poisoning caused by dicoumarol, a vitamin K antagonist.
Vitamin A is essential in the diet of cattle. Cattle convert carotene from leaves of plants to vitamin A in the wall of the small intestine. Vitamin A is necessary for vision, maintenance of epithelial tissue and mucous membranes, bone development, and immune function. Vitamin A is fat-soluble and stored in the liver when daily intake is three to five times greater than requirements. Mature cows can store up to four months of vitamin A. Under ideal conditions, cattle fed good-quality hay during the winter will have adequate vitamin A levels from carotene in hay and accumulated liver stores.
When conditions are less than ideal, vitamin A supplementation is required to maintain proper health and reproductive performance of the cow and normal development and health of calves. Drought conditions decrease the amount of carotene in plants limiting the ability of cows to accumulate liver stores while grazing. Forage harvested during drought also contains low carotene levels, decreasing the ability of cows to consume enough vitamin A during winter feeding. Another complicating factor is drought-stressed forages with elevated nitrate levels, thought to destroy carotene and vitamin A in the digestive tract and increasing requirements for vitamin A by depressing thyroid function.
Some of the problems encountered when nutrition is compromised during grazing season and not corrected during the last half of gestation are:
1. Increased rate of dystocia (calving difficulty)
Underfeeding late-gestation cows leads to more weak calves and stillbirths, often due to prolonged labour. Weak calves are more likely to get sick and die, and have decreased performance out to weaning and beyond. Cows in body condition 2.5 or 3 deliver more live calves compared to cows in body condition 2 or less.
2. Weak calves and hypothermia (inability to maintain body temperature)
Birth weights of calves will decrease, as does the storage of brown fat used to generate warmth. Both are important factors in calf vigour and survivability short term and reducing sickness and death rates longer term. Inclimate weather, poor housing, and the inability or desire of cows to seek shelter during calving all contribute to cases of hypothermia.
3. Sick calves
Low birth weights and reduced vigour increase the chances of calves not getting colostrum in time. A compounding factor: cows that are nutritionally deprived cannot produce quality colostrum in sufficient quantities. Both problems lead to the failure of passive transfer of protective antibodies. Without antibodies, calves are more likely to get sick and die. Even if calves survive an illness, performance is affected out to weaning and beyond.
4. Decreased response to vaccines
Response to vaccines administered during pregnancy (e.g. scours) is negatively affected in undernourished cows. Vaccinating cows to protect calves through colostrum will only work when cows are on a proper plane of nutrition. Without adequate colostrum, calves fail to respond to vaccines administered after calving. The result: fewer and lighter calves at weaning.
Females in poor body condition don’t breed back readily. A drop in body condition below 2.5 can reduce conception rates by 15 per cent. Dystocia rates also increase as body condition drops.
6. Replacement heifers
Calves that receive poor or inadequate colostrum, whether or not they get sick, do not grow as well as calves that get high levels of immunity through colostrum. The difference in growth extends into the feeding period for stocker calves and translates to increased time to breeding and time to mature weight in replacement heifers. Research suggests that cow nutrition during gestation has a long-term impact on growth and fertility of female offspring, an important consideration when retaining replacement heifers.
Feeding costs are a major expense in cow-calf herds. Selecting cost-efficient winter rations becomes imperative, but making sure nutrient requirements are met is critical to future profitability. An investment in rations that are right today pays dividends for years to come.