Study the possibility of transmission of immunity through colostrum and the change of colostrum compositions in fat-tailed sheep under the influence of feed restriction during prepartum

The transition period between pregnancy and lactation in mammals due to increase in the fetus energy and/or other nutrients requirements, and also onset of copious milk production is faced with an increase in energy demand, and in most cases according to inability to supply such requirements, animal goes down in negative energy balance (Drackley 1999; Zarrin et al 2017; Hernández-Castellano et al 2019). Lack of sufficient feed or balanced diet at the end of pregnancy leads to lack of growth and development of udder tissue during dry period, and consequently, decrease in milk yield and changes its composition during the next lactation period (Huang et al 2014). Physio-chemical properties and even yield of colostrum could be affected by production, nutrition, breed, dry period, seasons, litter size, parity and animal health status (Caja et al 2006; Romero et al 2013). However, colostrum composition and consumption during the first two days suckling lambs or goats, reduces the mortality rate as a result of antibacterial factors content. Therefore, the survival of newborns significantly depends on the 1- quality that could be measured by its immunoglobulin content, and 2- quantity of the consumed colostrum which leads to the recommendation of enough colostrum feeding; the colostrum quality might be measured by different methods (Arguello et al 2004; Keskin et al 2007). Recently refractometer has been used as a practical tool with easy and high accuracy, to determine colostrum quality (Murrill et al 2015; Castro et al 2018; Kessler et al 2021). The present study has been designed and implemented with the two objectives of investigating the effect of feed restriction around parturition on the changes in colostrum content in the first 72 hours of lactation and also studying the amount of immune transmission through colostrum using a digital refractometer device.

Twenty pregnant fat-tailed ewes were allotted to two experimental groups of Control, (n=10) and feed restriction (Restriction; n=10). After adaptation, during the pre-partum period, the control group from five weeks before parturition to parturition (-5 to -1) were fed with 100% of the balanced ratio. Restriction in the same period during the first to fifth weeks of the study were fed with 100, 50, 65, 80, and 100% of the recommended ration, respectively. The same nutritional program was repeated from the first to fifth week after parturition for the both groups (1 to 5). Ewes were sampled for blood weekly. Colostrum and lamb blood were taken at zero (parturition), 1, 12, 24, 36, 48 and 72 hours after parturition. Brix percentage was measured in blood samples of ewes and lambs as well as colostrum from both groups using a digital refractometer. The main contents of colostrum were measured and the data were analyzed based on the Mixed model procedure of SAS.

Feed restriction decreased the blood Brix percentage compared to Control (P<0.05). The Brix percentage in Control did not change during the experimental weeks, except for the last week of the trial. Feed restriction, sampling time and their interaction did not have any significant effect on blood Brix percentage of lambs in the both Control and Restriction. Feed restriction affected the Brix percentage of colostrum and this value showed a tendency to increase in the restriction group compared to the control group (P=0.07). There was no significant difference between the two udder quarters in the control group and the Brix percentage was the same during the experiment in both of them. Unlike the control group, in Restriction, the percentage of Brix in the left and right quarters were different, although the right quarters showed a higher Brix percentage (P<0.05). The Brix percentage started to decrease from 12 hours after parturition in both groups and both quarters compared to the initial time, nevertheless, it had a higher value compared to the following hours (P<0.05). The decreasing trend continued until 36 hours after parturition in the Control (P<0.05). There was no significant change in Brix percentage in the Control from 36 hours of lactation until the end of the experiment. Fat changes showed same pattern in the both experimental groups. The percentages of lactose, protein, solid non-fat, and density were higher at the beginning of the parturition, and started to decrease from 12 h after parturition in the both groups. Based on the results obtained in the current study, it can be concluded that the concentration of biological molecules in colostrum is at its highest at the parturition time during the first 24 hours after parturition. Moreover, their concentrations during sampling (72 h after parturition) were higher than the milk samples at the first week after the parturition (Zarin et al. 2021). Therefore, it can be concluded that mammary secretions are considered as colostrum until the end of the first day and as transfer milk until the end of the third day (Romero et al. 2013; De la Vara et al. 2020) and from one week after parturition it turns into milk. Feed restriction decreased the Brix percentage in the blood of ewes and this led to a decrease in colostrum production in this group, but despite, the Brix percentage of colostrum production was not affected by the two groups and even in the restriction group it tended to increase. Based on the present results, it can be deduced that fat-tailed sheep use their energy reservoirs to produce high-quality colostrum and transfer nutrients and especially immunoglobulins to newborns in the shortest time.