الفهرس 
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Abstract
The current study was carried out at El-Sero Animal Production Research Station, Animal Production Research Institute (APRI) Agricultural Research Center, Ministry of Agriculture, Egypt, in cooperation with the Department of Animal Production, Faculty of Agriculture, Mansoura University, Egypt Objectives:The study investigated the effect of different somatic cell count (SCC) classes on milk production traits and growth of Zaraibi does and kids at three distinct physiological stages during lactation.Animal and samples:A total of 150 milk samples obtained from 50 goats at milk peak, kids weaning, and mating periods (days of 50, 100 and 150) were analyzed. The goats were selected based on strict criteria, including the same age, kidding date, low milk SCC, and no udder problems.The goats were divided into three classes based on overall milk SCC values:- CLASS 1: SCG1 (≤315x103 cells/ml).- CLASS2 : SCG2 (316-335x103 cells/ml).- CLASS : SCG3 (>335 x103 /ml).These three stages were specifically chosen to provide a more comprehensive understanding of the changes in body weights, milk yield and composition by SCC levels throughout the lactation period.Effect of SCC classes:Growth performance growth performance of Zaraibi goats categorized into three different SCC classes.The does’ birth body weights in SCG1 and SCG2 are significantly higher (p=0.043) compared to SCG3.Similarly, the average body weight of does in SCG1 and SCG2are significantly higher (p=0.005) than SCG3.However,there is no significant difference in the birth and weaning weights of kids as well as birth type among the SCC groups.Daily milk yield, days in milk, and SCC for Zaraibi goats.The total milk yield is significantly higher (p=0.041) in SCG1 compared to SCG3, while SCG2 falls in between.There is no significant difference in the days in milk among the SCC groups.The daily milk yield tends to decrease as the SCC increases, although the difference is not statistically significant.The SCC count in milk is significantly higher (p<0.001) in SCG3 compared to SCG1 and SCG2.The Log SCC values show a similar pattern, with SCG3 having the highest value.Milk composition.The milk composition of Zaraibi goats based on SCC classes.The fat content in milk is significantly higher (p<0.001) in SCG3 compared to SCG1 and SCG2.There is no significant difference in protein and lactose percentages among the SCC groups.The ash and total solids content in milk are significantly higher (p<0.001) in SCG3 compared to SCG1 and SCG2.The solid not-fat percentages do not show significant differences among the SCC groups.Daily milk yield At all the lactation stages, the daily milk yield could be found significantly similar between SCG1 and SCG2, while decreased ( p≤ 0.004) by increased SCC(SCG3 , >335 x103 cell / mL milk).However, at 50 days of lactation, the daily milk yield decreased (p=0.001) by 24.6, and 24.5 moving from SCG1, and SCG2 to SCG3, respectively.While at 100 days of lactation, it decreased (p=0.003) in SCG3 than SCG1, and SCG2 by 22.0 , and 20.8 , respectively. The highest decrease (p=0.004) of daily milk yield in SCG3 was at 150 days of lactation by 26.7 , and 25.5 compared to SCG1 , and SCG2, respectively. On the other hand, in 50, 100, and 150 days of lactation the average milk losses were0.466, 0.326, and 0.302 kg milk, respectively, when moving from SCG1 and SCG2 to SCG3.The SCC and logSCC values were differed (p<0.001) among SCC classes obtaining similar trend across 50 and 100 days of lactation. While in 150 days of lactation, there was no significant difference between the SCG1 and SCG2 classes in the SCC and log SCC values, but both were significantly lower (p<0.001) than the SCG3 class by 12.34 and 7.13 , respectively for SCC values.Milk component.Although the percentages of milk components differed during the stages of lactation, the same trend in terms of significant differences was found for thedifferent SCC classes.However, the greatest values for all milk components were observed in SCG3. With no significant difference between SCG1 and SCG2, the milk fat, ash, solid not fat, and total solids percentages were significantly higher (p≤ 0.032) in SCG3 than both SCG2 and SCG1 classes.The percentage of protein and lactose did not significantly change between the SCC classes in the different stages of lactation.Does body weight.Among different SCC classes and stages of lactation, the does’ weights ranged from 31.50±0.557 to 34.17±0.771 kg. Although there were no significant differences for all the studied growth traits with the levels of SCC during the different stages of lactation, there are some differences between those levels.It is evident that the does’ body weights in the SCG3class are lower than those inboth theSCG1 and SCG2classes. On the other hand, the kids’ body weight, growth rate, and weight gain differed among SCC classes, with the highest performance for SCG3 andthe lowest for SCG1.4.2. Changes by stages of lactation:The daily milk yield, SCC, and logSCC of different somatic cell count classes by stage of lactation. The most noticeable for all groups, a gradually decrease (p<0.001) in daily milk yield and gradually increases (p<0.001) in SCC, and logSCC values were found by lactation stage.Daily milk yieldHowever, between 50 and 150 days of lactation, the daily milk yield decreased by about 38.61%, 39.49%, and 40.31% for SCG1, SCG2, and SCG3, respectively, and the SCC values increased by about 17.45%, 13.34%, and 9.68%, respectively.Milk composition bThe milk composition of all SCC classes followed the same pattern by lactation stages (Table 5 and Figure 2). The fat, protein, and total solids percentages were higher (p<0.001) in 150 and 100 days of lactation than in 50 days. The ash, and solid not fat obtained higher percentages (p<0.001) in the 150 days of lactation than in 100 and 50 days of lactation in all SCC classes. On the other hand, lactose percentages of SCG1, and SCG2 did not significantly change by stage of lactation,while SCG3 was higher(p<0.001) in 150 days than in 50 days of lactation.The does’ body weight.The does’ body weight of all SCC classes did not statistically change by stage of lactation.However, between 50 days and 150 days of lactation, the kids’ body weight increased (p<0.001) by about 51.55%, 51.20%, and 52.77%, for SCG1, SCG2, and SCG3, respectively, and the kids’ growth rate decreased (p<0.001) by about 30.14%, 30.16%, and 26.42%, respectively.However, the kids’ weight gain of all SCCclasses decreased (p<0.001) between 50 days and 100 days of lactation, but thereafter, insignificant differences were found between 100 days and 150 days of lactation.The correlations between SCC and productive traits as well as milk composition.There is a negative correlation (p≤0.034) between SCC and does’ birth body weight, total milk yield, daily milk yield, and birth type.Positive correlations (p<0.001) are observed between SCC and fat, protein, ash, solids not-fat, and total solids in milk composition.Overall, the findings suggest that SCC level of > 335x103 cells/ml has a significant effect on milk production and composition, but not on growth performance.ConclusionCurrent results reported that the threshold of SCC >335×103 cells/mL was determined as an indicator of a change in Zaraibi goats’ milk production and composition. The effect of SCC class (>335×103cells/mL) on milk composition was more pronounced for percentages of fat, solid not fat, and total solids than protein and lactose. Moreover, it showed more milk loss by lactation stage than lower SCC classes.