| Abstract |
This work was carried out at Mehallet Mousa Experimental Station (Northern region of Nile-Delta, Egypt. Kafr EI-Sheikh governorate, Animal Production Research Institute,
Agricultural Research Center, Ministry of Agriculture. The experimental work was extended for two years to cover both mating season ( September - October) and lambing season (January-February). The main objective of this work was to study the performance of Romanov and its crosses with Egyptian Rahmani local breed up to weaning with particular reference to mortality rates.
A total number of 180 ewes of different genetic constitution and their lambs (246) were used in this study The results are presented in four sections; the dam performance, the growth performance of the lamb, the metabolic activity of the lambs and the mortalities of the lambs, rates and ages.
The main results summarized as follows:-
Conception rate of ewes of 1/2 Romanov was the highest followed by Rahmani while pure Romanov showed the least success, 84,82 and 67% respectively.
Rahmani dams had the highest body weight at mating than 1/2 Romanov and pure Romanov dams, 46.0, 45.0 and 410 kg, respectively. At late pregnancy the weights of 1/2 Romanov and Rahmani dams were approximately the same while that of Romanov dams was
the least, 52.3, 52.0 and 45A kg, respectively. The same trend of genotypes appeared for lambing weight, 44.0,44.8 and 37.8 kg, respectively. The increase in dams' weights which occurred from mating to late pregnancy was the highest in 1/2 Romanov followed by Rahmani, the Romanov ewes showed the least increase, 7.2, 6.6 and 4.4 kg, respectively. After delivery all genotypes showed decrease in body weight being great in pure Romanov (8%).
Romanov ewes gave the highest litter size followed by 1/2 Romanov while Rahmani gave the smallest litter size, 2.0, 1.7 and l.4, respectively. Quadrate and triplet offsprings were more in pure Romanov than 1/2 Romanov dams while there were neither quadrate nor triplet 1/2 Romanov lambs as they are born to pure Rahmani dams.
Birth weight of 1/2 Romanov lambs was the highest followed by 1/4 Romanov and pure , Romanov, 3.322, 3.030 and 2.278 kg, respectively. Genotype and type of birth had significant effect on birth weight (P<0.01)
Weaning weights of 1/4 and 1/2 Romanov lambs were approximately the same and both were greater than that of pure Romanov lambs 11.6, 11.4 and 10.5 kg, respectively, genotype had no significant effect on weaning weight. Daily gain of 1/4 Romanov lambs was the highest followed by 1/2Romanov lambs while pure Romanov lambs showed the least gain 158,144 and 136 g/d, respectively. Body temperature of lambs Survived till weaning (STW) at 6:00h was the highest in 1/4 Romanov followed by pure Romanov while 1/2 Romanov showed the least value, 38.6, 38.4and 38.3 °C, respectively. At 14:00h 1/4 Romanov had the highest temperature then Romanov and pure Romanov, 38.6, 385 and 38.4 °C respectively. Glucose concentrations in lambs survived till weaning (STW) were higher in pure -Romanov and 1/2 Romanov lambs than in lambs which died before weaning (DBW) at all ages. In 1/4 Romanov the concentrations were approximately, the same at I day old, 104.0 vs. 105.5 mg/dl respectively and very close at 3 days of age, even slightly higher in the dying lambs, 85.6 vs. 92.8 mg/dl . 2 and 3).
Total lipids concentrations in STW pure Romanov lambs were clearly higher than in DBW lambs at 1 and 14 days old, while the concentrations on the third, 7th and 30th days were almost equal in the two categories. In 1/2 Romanov and 1/4 Romanov lambs the on centrations were higher in STW than in DBW lambs at all ages except on the 3rd day while the concentration were equal in the two categories of 1/2 Romanov and lower in the 1/4Romanov.
Plasma free fatty acids concentrations of STW Romanov lambs and 1/2 Romanov lambs were lower than that of DBW lambs at all ages, except at 30 days old in pure Romanov.
In the three genotypes the concentrations of plasma lactates were higher in the STW lambs than in DBW lambs except in few cases. In general there was a trend of successive decrease in the concentration with age progress. The 1/2Romanov lambs had lower concentration than pure and 1/4 Romanov lambs.
Thyroxin concentrations were higher in STW Romanov lambs than DBW lambs at 7, 14 and 30 days old. On the contrary it were lower at the earliest ages, I and 3 days old. The STW 1/4 Romanov lambs had higher concentrations than DBW lambs at early ages, 1,3 and 7 days old, while it had lower values at 14 and 30 days old. In STW 1/2 Romanov lambs T4 concentrations were higher than in DBW lambs at all ages, except at 7 days old.
Concentrations of T3 in STW pure Romanov and 1/4 Romanov lambs were higher than In DBW lambs at all ages. In contrast the STW 1/2 Romanov lambs had lower concentration than DBW lambs at all ages. Mortality cases recorded by autopsy indicated that the predominant case was pneumonia which accounted for 42%. Digestive defects cases were 17% and pneumonia- digestive deficits cases were 21 % while other cases were 20%.
Still births percentage in 1/2 Romanov lambs were the highest, followed by pure Romanov lambs and ¼ Romanov lambs 13.8, 9.8 and 8.3%, respectively.
Mortality rate (percentage) of pure Romanov lambs was greater (almost double) than -those of 1/2 Romanov or 1/4 Romanov lambs 50.0, 25.7 and 25.4% respectively.
Average birth weight for STW lambs were 2.401,2.884 and 3.346 kg for Romanov, ¼ Romanov and ½ Romanov respectively. and average birth weight of DBW lambs were, 1. 890, 2.774 and 2.898 kg.
Distribution of lambs' mortality according to the age at death in pure Romanov, ½ Romanov and 1/4 Romanov showed that the critical period for ½ Romanov lambs death is during the age 14-30 days (22%, 50% and 36% for the three genotypes respectively) Pure and ¼ Romanov showed the critical period within 30-60 days (50% and 38% respectively).
The glucose level is particularly important in the prevention of hypothermia, so hypothermic lambs were characterized by very low levels of glucose. Glucose level in the last sample taken before death indicated that there was a drastic decrease in plasma glucose levels, Some lambs showed a decrease in all energy substrates. There was an opposite trend between glucose and lactate concentrations in the same blood sample.
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