بررسی اثرات طول مدت شیردهی و استفاده از شیر گاو به‌عنوان جایگزین بر عملکرد بره‌های نژاد افشار-زل

Introduction: Separating the lambs from the ewes as soon as possible will make the ewes return to a suitable physical condition and prepare for the next pregnancy. Early weaning may be defined as the withdrawal of Local sheep breeds are characterized by their lower the milk supply before the time when weaning would normally occur. The success of early weaning must depend partly upon the speed with which the rumen develop in both lambs and calves and partly upon the level of milk production of the dams, of production from the early local weaned lambs. who also reported that rumen function develops rapidly after birth until, at about 8 weeks of age, the grazing lambs can digest herbage with the efficiency of an adult.
Stress in lambs or even older sheep may be associated with management procedures, malnutrition or poor weather (Demeler, 2005). Weaning may also constitute an important stress for ewes and lambs (Orgeur et al., 1999). In cattle and sheep behavioural responses to weaning (e.g. vocalisation and agitation) as well as blood parameters (e.g. cortisol) were observed and measured for several days or weeks (Veissier and Le Neindre, 1988, Schichowski et al., 2008). In sheep, both ewes and lambs express their distress by an increase in bleating and locomotion activity (Alexander, 1977, Torres-Hernandez and Hohenboken, 1979). Some stressors may induce suppression of the immune system with negative effects on animal health, welfare (Orgeur et al., 1999), and performance, as the release of glucocorticoid hormones coincides with a decrease in growth hormones (Kuhn et al., 1990). An alteration in growth rate may also result from the decrease of the quantity of ingested food or from an impairment of digestive function caused by weaning stress (Dantzer and Mormède, 1983).
Nutrition of the lamb during its first 4 weeks of life depends completely on the dam's milk (Burris and Baugus, 1955) and thus the lamb live weight gained is related to milk production and possibly to the composition or milk quality produced by the dam (Neidig and Iddings, 1919). After the first month, the amount of milk produced by the ewe is no longer sufficient to meet the nutritional requirements of the lamb, and the offspring gradually start to consume other solids (Banchero et al., 2005).
In Assaf flocks, artificial rearing with milk is commonly used either for avoiding transmission of diseases (e.g. Visna-Maedi) or to obtain a greater amount of milk, if market price of milk is high. Moreover, through artificial lactation controlling milk intake and, to a certain extent, the length of the rearing period could be made easier. It might thus be possible to get the maximal incomes from the sale of the lambs provided carcass and meat characteristics were not affected. There are several studies comparing performance and meat quality of naturally and artificially reared lambs of local breeds (Osorio et al., 2006) but there is no information about the effect of rearing system on performance and meat quality of Assaf lambs. Food or energy consumption is closely related to the metabolic weight of the animal. Most of the available estimates about the amount of fodder consumed by cattle and sheep in the pastures of the western regions of the United States are between 40 and 90 grams of dry matter per 0.75 kg of live weight or from 1 to 2.8 percent of body weight (Sadeghi Menesh, 2015). Early separation of lambs from ewes and feeding them with milk substitute is common in the world today. In a group of commercial milk substitutes, cow's milk powder is part of the main ingredients. The results of a research (Rodriguez et al., 2008) showed that the use of enriched cow's milk compared to the use of ewe's milk reduces the growth of lambs.


Materials and methods: In this study the effects of weaning age of lambs that sucked ewe milk naturally or cow milk artificially on the lamb average live body weight (ALBW) gain has been experimented for 140 days. 18 male and female Afshari – Zel crossbred lambs at 3±1 days of age placed in a randomized complete block design. Treatments were lambs sucking ewe milk naturally for 70 days (T1), lambs sucking ewe milk naturally for 90 days (T2) and lambs sucking natural cow milk artificially as milk replacer for 70 days (T3). Each treatment had two blocks of male and female sex in which there were 3 replications. Lambs were weighed in at 30, 60, 90, 120 and 140 days after birth. A starter concentrate contained 3.2 (Mcal.) ME and 18.8% CP per 1 kg DM was available 10 days after birth. In the fattening period a concentrate contained 3.1 (Mcal.) ME and 17.7% CP and a forage part contained 2 (Mcal.) ME and 14.3% CP per 1 kg DM was available. Daily weight gain was calculated by dividing the initial weight from the final weight by the duration of breastfeeding. Also, the metabolic weight of the lambs was calculated from the live weight of each animal to the power of 0.75.

Results and Discussion: The results showed there was no significant difference between male and female ALBW within each group at various weighing times. Also, lambs that sucked ewes for 70 days or 90 days had similar ALBW. But lambs that sucked cow milk for 70 days had a reduction in ALBW in comparison with T1 and T2.
Conclusion: In general, the findings of this research showed that consumption of cow's milk by nursing lambs reduced their weight compared to when they consumed milk.