Nutritional Aspect of Heifer Management to Reduce Age at First Calving and Cost of Heifer Production
Heifers are future herd of a dairy farm. They must be produced to replace the uneconomical females of the farm through voluntary culling. Production of heifer is most expensive part of the dairy farm operation. It requires more inputs for a longer period of time with no visible returns. The feed and management program for replacement heifers will have a lifelong effect on their productivity. It will determine how young they may be bred; whether they calve late, early or not at all; whether they are poor milkers or good milkers; the weaning weights of their calves; and how long they remain in the herd means longevity of heifer. Feed accounts for 50% to 70% of the cost of raising replacement heifers; hence, it is important to save on feed during the growing period and reduce cost of rearing without any adverse effect on health and reproduction. It is even more important to know whether their performance as adult animals can be enhanced by proper nutrition and management. Age at puberty is negatively correlated with plane of nutrition. Balanced feeding, proper management and disease resistance can be helpful in reducing the age at first calving. Proteins and energy are most critical nutrients influencing the growth of calves to become heifers. However, minerals and vitamins are also important. Other than essential nutrients, there are performances modifiers that can accelerate the growth rate of calves and help attain early puberty in heifers. The major issue is the lower growth rate of calves during early months of their age and just after weaning. Lower growth rate in the early life of the calves is either due to underfeeding or imbalanced feeding. The goal of replacement heifer selection is to identify heifers that will develop into high-output, low-input cows with longevity; and ultimately, high milk producer cow. Replacement heifers should be selected and managed so they will calve early in the calving season, provide adequate milk production, and rebreed and calve every year. Heifers bred as yearlings to calve as two-year-olds will produce an extra calf in their lifetime compared with heifers calving first as three-year-olds, without detrimental effects on mature size, milk production, or calf weaning weights. The type of management heifers receive from birth to breeding has a great influence on their lifetime calf production. It is important that heifers be selected and developed properly for efficient and optimum production over 7 to 8 calf crops. Development programs should focus on nutrition to achieve puberty by 12 to 14 months or younger with additional emphasis on early conception and rebreeding the following year. Care must be taken to ensure minimum calving abnormalities through heifer and sire selection. Do not provide heifers creep feed during the suckling period, as fat may be deposited in the developing udder, lowering subsequent milking ability.
REDUCING COST OF HEIFER PRODUCTION
Heifers production is the most expensive component of the dairy farm operations. Poor nutrition and poor growth rate resulting in delayed age at maturity in our local dairy animals further aggravates the situation. However, cost of heifer production can be reduced through better management, balanced feeding and better health care. Selection for higher milk yield is likely to have a favorable impact on age at first calving. Currently age at maturity in buffalo and Sahiwal cow can be reduced to 2 and 1.5 years, respectively, with better feeding and management. Protein and energy along with minerals are the most critical nutrient affecting the weight and consequently age at puberty in heifers. Protein levels more than current recommendations of NRC for dairy cattle can reverse the adverse effects of high plane of nutrition on udder development. Performance modifiers accelerates growth rate to reduce the age at maturity is also helpful provided they do not adversely affect development of secretary tissue of udder for future milk production. Judicious use of balanced feed has led to reduced age at puberty in exotic dairy heifers. These data can be used to device optimum heifer production systems in the our country. The success of attaining target weights for replacement heifers depends upon a soundness of nutritional program that balances rations around forage quality. Knowing forage quality means knowing whether protein, energy and minerals must be supplemented. Without forage testing, feeding a balanced ration is impossible; subsequently, heifer performance may suffer, and costs may be higher than necessary. Periodic weighing is helpful in determining whether heifers are gaining at calculated rate or not. Make sure weights are taken at the same time of day and use group weights because gut fill can cause bias errors in weights. Some reproductive cycling should be observed in the heifers by 40-60 days before breeding season; if not, additional grain or high energy supplement should be provided. However, for determining of solid recommendations on optimum heifer production requires well planned research to see the effects of proteins, energy, minerals and other performance modifiers for economical heifer production in our country.
NUTRITIONAL STRATEGIES AND THEIR IMPACT
Effect of suckling and hand feeding on calf health-
Suckled calves are healthier than weaned calves. As per a experiment, conducted by Ryle and Orskov (1990) have advice given to farmers in developing countries to wean calves early in order to increase the amount of saleable milk is inappropriate. They also summarized the results of various studies on calf rearing. Studies showing more economic returns to wean calves at the youngest age possible are also there but that does not apply to the farmers in resource-poor developing countries. This is mainly due to the unhygienic conditions prevailing during artificially feeding the calves. Furthermore, maintenance of desired temperature of milk fed to calves especially in winter is difficult. A study at Animal Sciences Institute, National Agriculture Research Centre, reported that calves reared by restricted suckling of their dams had better growth rate (552 vs 370 g/d) on less milk consumed (2.7 vs 3 kg/d) than those given milk through nipple pale. Holstein crossbreds in Vietnam, have also reported similar results. It was found that weight gain of direct suckling calves was higher (445 vs 422 g/d) than that of artificially reared calves. The milk consumed per kg of weight gain was less in suckling calves than on artificially reared calves (4.2 vs 4.7 kg respectively). In the light of these studies, the farmers in developing countries should follow the indigenous practices that can enhance daily growth rate to get a healthier calf crop. Further research studies are also needed to test the hypothesis whether weaning should or should not be practiced in Sahiwal cattle or Nili-Ravi buffalo that have a very strong mother instinct to milk let down in the presence of calf which if weaned results into either abandoning of the lactation or milk let down through oxytocin.
Effect of protein, energy and minerals in calf starter ration
In our country, fodder is usually available for calves rearing with limited amounts of concentrates low in protein and energy before and after weaning. This is one of the reasons for lower growth rate and delayed age at puberty in heifers. This issue is short out by research workers by various experiments in our country. Calf starter ration containing CP% and TDN%, 17, 78 and 16, 72, respectively, a higher daily growth rate (471 vs 336 gm) has been observed in buffalo calves (Ahmad and Jabbar, 2000). Beyond the level of 20% CP, no additional response was observed on the daily growth rate of calves. In our country, where there is no check on quality of concentrates for ruminants, offering a quality concentrate supplement with higher protein and energy may accelerate growth rate in the replacement calves with positive effects on reducing the age at puberty. Macrominerals as well as microminerals have great impact on growth of calves and significantly reduce the age at first calving. Calves, heifer and lactating animals should be supplemented with 2% area specific mineral mixture in their diet. It reduces the stress on animal and improves the health and production.
Effect of concentrate feeding on puberty
In a study in Nili-Ravi buffalo heifers fed green fodder only and fodder plus concentrate diet at rate of 1% of body weight in other group of buffalo heifers. They found that age at puberty was reduced by 8 months in heifers fed fodder plus concentrate than those fed fodder only. The concentrate ration had 15.4% CP and 65% TDN. Age at puberty could be reduced by one month through additional concentrate feeding for a few months before the onset of puberty in Nili-Ravi buffalo heifers. Supplementation of concentrate with green fodder particularly in summer season reduced the age at puberty in buffalo heifers. In spring born Hereford x Angus cattle feeding high starch diet (73% corn; 53% starch) 60 days before breeding may increase the incidence of puberty during breeding of heifers that have inadequate yearling weight. Furthermore, the CP and energy concentration of the concentrate supplement are still less than the recommended levels for a total mixed ration for temperate breeds. This information provides further room for reducing the age at puberty by providing a supplement with higher CP and energy concentration or a total mixed ration.
Effect of bST on age at puberty
Pituitary, a small gland located at the base of the brain, secretes Somatotropin hormone from the anterior part which is transported by the blood to various body organs where it has its biological effects. It has been extensively used in ruminants for promoting growth and production. Radcliff et al. (1997) reported that injection of bST (25 μg/kg of body weight) in Holstein heifers increased daily body weight gain and weight at puberty by 10%, and 25 kg, respectively and reduced the age at puberty by up to 24 days. Also heifers with initial body weight of 135 kg, injection of bST at a rate of 25 μg/kg of body weight at a high plane of nutrition (CP: 19.7% and energy 2.8 Mcal/kg) reduced the age at puberty in Holstein heifers by 90 days. bST altered the intermediary metabolism in a manner that increased lean tissue and decreased fat deposition.
Effect of antibiotics on puberty
Antibiotics are the product of variety of microorganisms that acts over other organisms. Feeding of ionphore antibiotics increases the efficiency of feed utilization in ruminant animals. Monensin feeding significantly decreased the age at breeding by 15 and 24 d and age at calving by 36 and 61 days for heavy and light Holstein heifers, respectively. In an earlier study, Mosley et al. (1977) reported that 92% of the heifers fed monensin reached puberty earlier as compared with only 58% of heifers in without antibiotic group, with no effect on weight gain. Similarly cows fed 200 mg of monensin per day shows lower age at puberty.
Effect of diet on mammary gland development
As the growth rate increases, the requirements of crude protein increase at a faster rate than energy requirements. Therefore, increased protein to energy ratio for rapidly growing heifers can alters the adverse effects of high energy diets on their mammary gland development. It has been found that feeding protein to energy ratios above NRC recommendations improved feed efficiency and increased average daily gain and mammary development. Thus, increased protein concentration in the ration of dairy heifers with high energy can reduce the age at puberty without adversely affecting the mammary gland development and its subsequent effects on milk production.
CONCLUSIONS
Improved feeding strategies have significant effect on puberty. Protein, energy and mineral supplementation significantly reduces the age at first calving without any adverse effect on heifer and resulting in higher milk producing ability with longevity. bST and Ionophore antibiotics can be used to decrease the cost of heifer production with enhance reproductive performance. Increased protein and energy ration in dairy heifers can reduce the age at puberty without adversely affecting the mammary gland development and its subsequent effects on milk production.
Compiled & Shared by- This paper is a compilation of groupwork provided by the Team, LITD (Livestock Institute of Training & Development)
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