September, 1954] A. A. ASKER, M. T. RAGAB AND A. E. BASTAWISY 141
Ewes that lamb during winter (October-March) are in a better condition before
lambing than those that lamb in summer since the former group have plenty of green
fodder (clover) to consume, and consequently they produce more milk. Lambs
born during winter have two advantages, i.e. their dams can provide them with
adequate amount of milk and they have also plenty of clover to consume. Con-
sequently they surpass lambs born in summer in weight and growth rate.
Wallace [1948] and Verges [1940] have shown that birth weight of lambs and
milk yield of ewes are affected mainly by the level of nutrition of the ewe during
the last six weeks of pregnancy. They have demonstrated also that vigour, growth
and development of lambs depend mainly on the milking ability of ewes as well as
on the amount of food available for lambs.
Hammond [1944] has stated that no one single factor affects growth rate of
lambs more than the milk supply of the ewes, and that the rate of growth of the
lamb is considerably affected by the amount of fibre in the food. Bonsma [1939]
and Wallace [1948], found a strong correlation between milk yield of ewes and
growth rate of lambs especially before weaning when lambs depend mainly on the
milk supply of their dams.
Although lambs dropped during summer have enough concentrates, yet their
ration contained hardly any green fodder. Under such conditions, the utilization
of the whole concentrates ration becomes less efficient than when the ration contains
enough green material, thus affecting the growth and development of lambs.
It is also feasible, that hot weather during summer at Giza (average temperature
26°C.), reduces the amount of milk produced by ewes lambing in summer. Con-
sequently the growth rate of their lambs is retarded. Such effect on milk yield in
dairy cattle has been reported by Espe [1946], who mentioned that high atmospheric
temperature seriously depresses milk secretion.
The level of nutrition is an important factor in determining the weight and
development of lambs. This was demonstrated by many workers who mainly
studied the effect of the year of lambing on lambs' weights. Hazel and Terril
[1945], Terril, et al. [1947], Asker, et al. (1953) and Daniel, et al. [1953], agreed to
that the year of lambing is an important factor in determining both weight and deve-
lopment of lambs. Years differ from one to the other in the amount of food avail-
able to the animals as well as the atmospheric temperature. These two factors
are in fact the main reasons of year to year variations.
It should be noted here, that some of the ewes that lambed in summer were
virgin and some others were lactating. No comparable group of ewes was available
in the winter-lambing group of ewes. This may be responsible to some extent for
the results obtained here. Nevertheless, the number of lactating and virgin ewes
was limited, besides that under the system of husbandry used in the two flocks,
it was impossible to secure lactating ewes that could lamb during winter time.
Therefore, it is not advisable to follow the summer-lambing practice unless the
farmer can provide both ewes and lambs with adequate food, including green
material. At any rate, the possibility of summer-lambing should be attempted in
the more favourable regions of the country, where the weather is milder and green
fodder is available during most months of the summer. Moreover, the effect of
summer-lambing on the longevity and fertility of ewes should be investigated.
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