Theme 19: Use of Supplements
Description
Generally in temperate regions, beef and milk were produced on extensive systems with forage from perennial pasture and natural grassland being the main component of animal diet. Supplementation on pasture was usually applied strategically to supply nutrients to grazing cattle only when forage availability was not enough to satisfy animal’s requirements. At present beef and dairy production systems have become more intensive and even when forage from pasture continue being the main component of the diet higher level of different type of supplement are fed to the animals. Intensive systems are characterized by a higher stocking rate capable of consuming the spring regrowth of pasture, and by an increment in the amount of supplement offered to the animal. Two factors affect nutrient intake when cattle on grazing are supplemented with concentrate: 1) substitution rate of pasture by concentrate, and 2) the depression on fiber digestion. On high quality pasture the effect of supplementation on substitution rate is more important than the effect on fiber digestion while in low quality pasture the opposite occur, it means the depression on fiber digestion is what more affect nutrient intake. In winter forage production is minimum and cattle is supplemented to maintain the stocking rate needed to graze efficiently pasture in spring. Corn silage is generally supplemented in winter and in this case animal performance will be affected by the energy contents of corn silage, which it will depend mainly on the grain content in the total plant and the digestibility of the rest of the plant. In autumn the grazing diet is usually unbalanced in term of energy and protein because an excess of degradable protein in temperate pasture normally occur causing high levels of ammonium nitrogen in rumen fluid. Starch contained in barley and wheat grain or in high moisture corn are more readily available at ruminal level that starch from dry corn or sorghum being therefore those grain a better energy supplement to cows on grazing in the fall. However in several trial trying to balance autumn pasture with readily available starch, even when some effect on ruminal level was observed, not always an effect on milk yield or body weight gain was obtained. Summer supplementation on beef production is generally done to increase body weight gain when quality of mature pasture decrease and to finish the animals with an optimum fat deposition before slaughtering. Due to the importance that meat quality and composition is getting in the international market, different type and amount of grain supplementation on grazing or finishing in feedlot will have to be considered in order to produce the type of meat that each specific market will demand. Beef from grazing steers had a lower content of cholesterol, a higher amount of n-3 linolenic acid and a lower n-6/n-3 linolenic ratio. Linolenic acid from pasture would be the source for this conjugated unsaturated fatty acid in beef. The importance of those fatty acids relay on their incidence in reducing the risk of arterial coronary diseases. Pasture-finished steers had lower predicted lean yields, smaller rib-eye areas, and darker colored meat than grain-finished steers. Although a yellowish fat was obtained in steers finished on pasture, grain feeding did not change fat texture, nor tenderness, juiciness, flavor and overall acceptability by consumers. Even when drylot steers had a higher performance and better carcass characteristics, compared to grazing steers, those parameters were improved when grazing was supplemented with grain. In dairy, considering the high losses of dietary nitrogen occurring in temperate pasture it could be suggested that the amount of amino acids reaching duodenum and available for absorption could be not enough to satisfy nutrient requirements of high yielding cows. However, responses to protein supplementation on milk production and composition are quite variable and generally disappointed. On milk quality, there is currently limited opportunity for dairy farmer with grazing systems to manipulate the composition of the N components in milk by supplementing different type of concentrate. As conclusion it could be said that there is not a unique approach to supplement animals on grazing. Each situation would require its own analysis to produce at the lowest cost the product that the specific marker requires.
Included in
Supplementation of Temperate Pastures
Generally in temperate regions, beef and milk were produced on extensive systems with forage from perennial pasture and natural grassland being the main component of animal diet. Supplementation on pasture was usually applied strategically to supply nutrients to grazing cattle only when forage availability was not enough to satisfy animal’s requirements. At present beef and dairy production systems have become more intensive and even when forage from pasture continue being the main component of the diet higher level of different type of supplement are fed to the animals. Intensive systems are characterized by a higher stocking rate capable of consuming the spring regrowth of pasture, and by an increment in the amount of supplement offered to the animal. Two factors affect nutrient intake when cattle on grazing are supplemented with concentrate: 1) substitution rate of pasture by concentrate, and 2) the depression on fiber digestion. On high quality pasture the effect of supplementation on substitution rate is more important than the effect on fiber digestion while in low quality pasture the opposite occur, it means the depression on fiber digestion is what more affect nutrient intake. In winter forage production is minimum and cattle is supplemented to maintain the stocking rate needed to graze efficiently pasture in spring. Corn silage is generally supplemented in winter and in this case animal performance will be affected by the energy contents of corn silage, which it will depend mainly on the grain content in the total plant and the digestibility of the rest of the plant. In autumn the grazing diet is usually unbalanced in term of energy and protein because an excess of degradable protein in temperate pasture normally occur causing high levels of ammonium nitrogen in rumen fluid. Starch contained in barley and wheat grain or in high moisture corn are more readily available at ruminal level that starch from dry corn or sorghum being therefore those grain a better energy supplement to cows on grazing in the fall. However in several trial trying to balance autumn pasture with readily available starch, even when some effect on ruminal level was observed, not always an effect on milk yield or body weight gain was obtained. Summer supplementation on beef production is generally done to increase body weight gain when quality of mature pasture decrease and to finish the animals with an optimum fat deposition before slaughtering. Due to the importance that meat quality and composition is getting in the international market, different type and amount of grain supplementation on grazing or finishing in feedlot will have to be considered in order to produce the type of meat that each specific market will demand. Beef from grazing steers had a lower content of cholesterol, a higher amount of n-3 linolenic acid and a lower n-6/n-3 linolenic ratio. Linolenic acid from pasture would be the source for this conjugated unsaturated fatty acid in beef. The importance of those fatty acids relay on their incidence in reducing the risk of arterial coronary diseases. Pasture-finished steers had lower predicted lean yields, smaller rib-eye areas, and darker colored meat than grain-finished steers. Although a yellowish fat was obtained in steers finished on pasture, grain feeding did not change fat texture, nor tenderness, juiciness, flavor and overall acceptability by consumers. Even when drylot steers had a higher performance and better carcass characteristics, compared to grazing steers, those parameters were improved when grazing was supplemented with grain. In dairy, considering the high losses of dietary nitrogen occurring in temperate pasture it could be suggested that the amount of amino acids reaching duodenum and available for absorption could be not enough to satisfy nutrient requirements of high yielding cows. However, responses to protein supplementation on milk production and composition are quite variable and generally disappointed. On milk quality, there is currently limited opportunity for dairy farmer with grazing systems to manipulate the composition of the N components in milk by supplementing different type of concentrate. As conclusion it could be said that there is not a unique approach to supplement animals on grazing. Each situation would require its own analysis to produce at the lowest cost the product that the specific marker requires.
