Influence of some Genetic and Non-Genetic Factors on Total Milk Yield and Lactation Period in Iraqi Awassi Sheep

| This study was conducted to evaluate productivity of Awassi sheep raised at the Research Station of Sheep and Goats (Abo Gharib) in the west of Baghdad, Iraq. A total of 369 milk records of the Awassi ewes collected during year of 2008 were used to investigate the effect of some genetic and non-genetic factors (group of dam, parity, month of birth, type of birth and sex) on total milk yield (TMY), and lactation period (LP). Data were analysed by using GLM in SAS program. Restricted Maximum Likelihood Estimation method (REML) was used to estimate heritability (h2) for milk yield an lactation period. Best Linear Unbiased Predication (BLUP) values were estimated for rams. Results revealed that total milk yield (TMY) and lactation period (LP) were 103.57±3.63kg and 107.44±1.47 days respectively. LP affected significantly (P< 0.01) by parity, group of dam (local and Turkish), month of birth and type of birth (single and twin), while the sex of birth was not significant. TMY was affected significantly (P< 0.01) by the same factors except the parity and sex of birth, which were not significant. Estimates of heritability for TMY and LP were 0.40 and 0.30 respectively. BLUP values of rams for total milk yield were between -33.61and 31.00 kg. These results point to a high genetic potential of Awassi sheep. Hence, it is imperative to apply selection programs to improve the productive performance of Awassi sheep in Iraq.


Advances in
85.80 to 142.00 days (Eliya and Juma 1970;Karam et al., 1971;Alkass et al., 2009;Al-Samarai and Al-Anbari 2009;Abd Al-Noor, 2011).The potential genetic ability of Awassi sheep for increasing milk production have been supported according to the genetic improvement programs that have been applied in Israel.Intensive selection within the Awassi breed has increased milk production in Israel from 297 kg in 1940's to over 500 kg in the 1990's (Epstein, l985;Galal et al., 2008).Thus, the objective of this study was to determine the level of influence of some factors on milk yield and lactation period, as well as to estimate the heritability of these traits as heritability is an important genetic parameter that must be taken into consideration when designing breeding programs for animal populations and the study also aimed to estimate Best Linear Unbiased prediction (BLUP) of sires for TMY.

MATERIAL AND METHODS
This study was conducted at the Research Station of Sheep and Goats, Abu Gharib, Ministry of Agriculture, Iraq.
A total of 369 records of productive performance of 369 Awassi ewes daughters of 66 sires were analyzed for one year (2008).The flock was kept in semi-shaded houses, grazed mainly on natural pastures and some green forage legumes and cereals during March-May.During June-November, the flock grazed on crop residues post harvesting with access to grazing a triplex shrubs, in addition to some supplements (250-500 gm/head) of feed concentrates according to their physiological status.In winter, the flock was fed 0.5-1.0kg concentrate of mixed grain in addition to 0.5-1.0kg of hay and straw.
Milk yield was measured weekly (Twice-daily).On the milk recording day, lambs were isolated from their dams, and dam's udders were evacuated handily from the surplus milk post lambs suckling, and milk produced was weighed and recorded.This method was routinely repeated till lambs were weaned.The flock included Local Awassi in addition Turkish Awassi which was exported from Turkey to improve the performance of local Awassi by mating.

statistical analYsis
Data were analysed using General Linear Model (GLM) in SAS program (2010) to investigate the effect of some fixed factors on: total milk yield and lactation period in Awassi sheep according to the following linear model: Where Y ijklm is the studied trait, μ is the overall means, P i the fixed effect of i th parity (i = 1 -2), X j the fixed effect of j th birth month (j = January, February and March), W k the k th effect of birth type (k = 1= single, 2 = twins), G l the fixed effect of sex of lamb and e ijklm is the residual effect.
Mixed model was used to estimate variance components using Restricted Maximum Likelihood Estimation (REML) method as following model: Where Y ijklm , μ, P i , X j , W k , G l and e ijklmn are the same in the first model, whereas S m is the random effect of sires.The same model was also used to estimate Best Linear Unbiased Prediction (BLUP) of sires for TMY using Proc mixed procedure in SAS program (2010).
Least square means were compared using Duncan test.et al., 2009).The effect of type of birth on TMY was significant (P< 0.05).TMY of ewes suckling twins (94.65 kg) was higher than that of ewes suckling singles (79.72 kg).Such increase was obviously due to increased stimulation of the udder.Similar results have been found by Macciotta (1999), Sakul et al. (1999), Alkass et al. (2009) and Kassem et al. (2010).On the other hand, the effect of sex of birth on TMY was not significant.Our results confirmed finding of Al-Samarai and Al-Anbari (2009).In present study, the overall mean of LP of Awassi was 107.44 days (Table 1), which was within the range of 85.80 to 142.00 days reported by previous studies (Eliya and Juma, 1970;Karam et al., 1971;Alkass et al., 2009;Al-Samarai and Al-Anbari 2009;Abd Al-Noor, 2011) for the same breed in Iraq.LP was affected significantly (P< 0.05) by parity (Table 3).The LP of second parity (100.58 days) was higher than first (88.63days) and third parity (85.78 days).Iñiguez and Hilali (2009) and Kassem et al. (2010).Our finding could be reflects the differences in genetic potential between local and Turkish sheep, in other words it seems that persistency of Turkish Awassi was higher than local Awassi, however this explanation need more studies to be determine.The effect of month of birth was significant (P< 0.01).Highest estimate of LP was found in January with reduction in estimation along with advancing sequence of months.This finding is consistent with Abdul-Rahman and Abbo (2013).In the finding of present study, the effect of type of birth was significant (P< 0.01  (2009), Mavrogenis (1996) and Hossamo et al. (1985) for the same breed.Whereas the estimate of present study was higher than 0.103 (Pollott and Gootwine, 2001), 0.25 (Pollott et al., 1998) and 0.26 ( Jawasreh and Khasawneh, 2007).The variation in estimates of heritability could be attributed to several factors: such as, method of estimating variance component, size of flock, breed of sheep but generally the estimate of heritability of TMY tend to be low for flocks under selection.Gootwine, (2011) stated that "In response to selection for high milk production in the Awassi, the genetic variation for milk production ability is expected to decrease in the selected lines.It is thus not surprising that heritability estimates for milk yield in the Improved Awassi dairy strain are low as compared to those in non-selected Local Awassi populations".The estimate of heritability of LP was moderate (0.30) which was consistent with 0.33 recorded by Al-Sa-

Table 1 :
Least square means of TMY and LP of Awassi sheep **Means with the different letters in same column differed significantly (P< 0.01); N.S=Non-significant

Table 2 :
Analysis of variance of factors affecting TMY in Awassi sheep

Table 3 :
Analysis of variance of factors affecting LP in Awassi sheep

Table 4 :
Heritability of TMY and LP in Awassi sheep

Table 5 :
BLUP values of sires for TMY and LP