Use of Wood's model to analyze the effects of milking methods on lactation curve in sheep
Introduction
The quantity of milk produced by ewes is the most important factor in determining lambs growth rate in commercial lamb production systems (Benson et al., 1999). Due to the influence of milk yield on weaning weight and due to the large variation in milking ability among the wide ranges of genotypes available in tropical and temperate areas, estimates of the amount of milk produced by lactating ewes provide information for the implementation of optimum management and feeding strategies for ewes and their lambs (Cardellino and Benson, 2002, Banda et al., 1992). Several methods of estimating ewe milk production have been reported which include weigh-suckle-weigh, hand milking, machine milking, and indirect assessment using body water dilution techniques (Doney et al., 1979, Unal et al., 2007).
Sheep's milk is very important for manufacturing some dairy products in Iran such as cheese, ghee, yoghurt and other fermented dairy products. It is also consumed by farmers as their main source of animal protein. Sheep represents an important part of the agricultural economy of Iran with an estimated 53,800,000 head, which produces 577,030 tons of milk annually (FAO, 2009). In Iran, sheep milk is about 22% of total milk production and 10% of World's sheep milk production (Haenlein, 2001). Makui sheeps are mostly kept by local pastoralists and on an extensive production system in North-western region of Iran. They are a multi-purpose (milk, meat and wool) breed and are fat-tailed, medium-sized (mature weight range of 46–49 kg), and annual greasy fleece weight between 1.2 and 1.5 kg, indigenous to the south-eastern region of Turkey, which are properly adapted to dry and hot climate conditions with low quality pastures. This breed is well adapted to harsh conditions and capable of production and reproduction under these circumstances.
Milk ejection is a neuroendocrine reflex; in which, oxytocin is released from the pituitary in response to tactile teat stimulation, and causes myoepithelial cells surrounding the alveoli to contract, which forcing milk stored in the alveoli into the mammary ducts and gland cistern (Lefcourt and Akers, 1983). Pituitary oxytocin is generally considered the only hormone capable of increasing milk production via stimulation of the milk ejection reflex. Ewes generally adapt quickly to routine milking in a dairy situation. However, ewes managed for commercial lamb production have no dairy experience, and some sheep may be extremely nervous on initial close handling. Adrenalin is known to be antagonistic to oxytocin, which is potent vasoconstrictor of mammary vessels released from adrenal medulla and this may affect the efficiency of the milking technique, and the level of oxytocin required for uniform milk let down (Morgan et al., 2000). Milk fat has been shown to be affected by the injection of oxytocin (Zamiri et al., 2001, Ribeiro et al., 2007). Oxytocinis responsible for milk ejection reflex and important for removing the maximum amount of fat (Labussière, 1988). In ruminant milk secretion rate is regulated by milk-borne negative feed-back (MBNF) mechanism (Linzell and Peaker, 1971, Bencini et al., 2003, Silanikove et al., 2010), this idea indicated the change in the frequency of mammary gland evacuation regulated milk secretion, so increase in milk frequency increases milk secretion rate. However, two mechanism of MBNF have been described (Linzell and Peaker, 1971, Silanikove et al., 2010) feedback inhibitor of lactation and plasminogen-plasmin system. The composition of sheep milk and its production per lactation are influenced by a large number of factors; the most important factors are breed, nutrition, health of animals, environment, ewes age and stage of lactation (Gonzalo et al., 1994, Kuchtík et al., 2008). There is no information available about the pattern of lactation curves in Makui sheep. Several models of lactation curves have been developed. The Wood's model (Wood, 1967) is the most well-known and commonly employed mathematical model. The shape of the lactation curve provides valuable information on the biological and economic efficiency of the animal to be used for genetic evaluations, health monitoring, rations formulation, feed management decisions and economic evaluation of different management schemes (Wood, 1967, Ruiz et al., 2000, Dag et al., 2005, Keskin and Dag, 2006). The objective of this experiment was to examine the effects of evacuation methods, ewes age and lactation stages on milk production and composition and application lactation curve of Makui sheep by Wood's model.
Section snippets
Experimental design
The experiment was conducted in the Production and Breeding Center of Makui sheep. 166 ewes (2 years old n = 66, 4 years old n = 17, 5 years old n = 58, 6 years old n = 25) of the Makui breed sheep, with the average 46 ± 2.5 kg body weight, which were selected from Animal husbandry farm, were used to evaluate the effect of milking method, ewe sage and lactation stage on milk yield, composition and shape of lactation curve during a 168-d lactation period. The animals were randomly assigned in two
Milk yield and lactation length by Fleischmann method
Least squares means and analysis of variance for milk production and lactation length, estimated by Fleischmann/really method comparing OT and HT ewes are shown in Table 1, Table 2. Average daily milk yield (ADMY), total milk yield (TMY) and lactation length (LL) affected by evacuation methods and ewes age (P < 0.0001). ADMY (g), TMY (kg) and LL (day) obtained by OT method was significantly (P < 0.01) higher than that obtained by HT method (Table 1). Ewes milked out with HT method had significantly
Discussion
Hand milking is a common way of milking in many Mediterranean countries, which is most often used for milking ewes in Iran by sheep farmers. Machine milking does not have relevant effects on ewe milk yield or on milk protein and fat content in comparison to hand milking (Casamassima et al., 2006). Hand milking releases more oxytocin than machine milking (Gorewit et al., 1992), indicating the importance of hand preparation of the udder for fast and complete milking; so, for milk measurement in
Conclusion
The majority of dairy ewes is managed under traditional systems and milked by hand. It can be concluded that, use of oxytocin for facilitating milk ejection on ewes is not adapted to the milking routine. Frequency of milking or complete evacuation of udder regulates the rate of milk secretion by milk-borne negative feed-back mechanism. Oxytocin has a dual effect on lactating mammary tissue mainly by its action on milk ejection via the contraction of myoepithelial cells maybe limiting the
Acknowledgement
The authors would like to acknowledge the assistance rendered by Dr Atashi (Shiraz University).
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