پژوهش های علوم دامی (Feb 2022)
The effect of feed restriction on body weight and blood metabolites in non pregnant fat-tailed ewes
Abstract
Introduction: Livestock systems in developing countries located in tropical and sub-tropical regions are heavily dependent on the natural resources (i.e. pastures). In these countries, decreased pasture availability and quality during the dry season have negative effect on performance and health of dairy ruminants. In these conditions, energy intake does not meet energy requirements for body maintenance, fetal growth and milk production, which results in negative energy balance, and high adipose tissue mobilization. Studies have shown that the risk of metabolic disorders would considerably increase if adaptation to NEB fails, affecting performance as well as overall health and welfare of animal. Fat-tailed sheep, such as the Lori-Bakhtiari and Turkey-Qashqai breeds, are raised in semi-arid regions of Eastern and Southern Africa, Central Asia, as well as numerous countries in the Middle-East. The common characteristic of all fat-tailed sheep is the deposition of a substantial amount of fat in the tail. Fat-tailed sheep are known for being highly resilient to harsh environmental conditions such as those related to the dry season such as water scarcity and low quality pastures and feedstuffs. According to the literature, fat depots are differently regulated in fat-tailed sheep compared to other sheep breeds during periods of feed scarcity. However, most of these studies have been performed in sheep breeds used for meat production. Material and methods: The present study was carried out in the experimental farm of Yasouj University (Naregah, Yasouj, Iran). All animal procedures followed the ethical law on Animal Protection and were approved by the Committee of Animal Experiments (Yasouj University, Iran). All ewes used in this study were visually healthy and had no signs of diarrhea. The present study was carried out to investigate the negative effect of a reduced energy intake on the body weight and blood metabolites of non-pregnant fat-tailed ewes. In this experiment, 10 non-pregnant fat-tailed ewes (Lori-Bakhtiari and Turkey-Qashqai) with average age 3.6 ± 0.3 y and BW 49.2 ±3.60 kg were used. During the trial, all animals were kept in individual pens (1.2 × 1.0 m2) located in a closed barn. Each pen was equipped with a separate drink and feed container. Two weeks before the start of the experiment all animals were fed with a total mixed ration (TMR) diet formulated to fulfill 100% of the energy requirements recommended by the NRC (2007). Then, animals were randomly allotted into one of the two experimental groups, including control (n= 5) and the feed restriction (n=5) groups. Ewes of the control group had ad libitum access to the diet from wk 1 to wk 5 (end of experiment). The feed restriction group was fed with a diet equivalent to the 100%, 50%, 65%, 80%, and 100% of the energy content of the dry diet on wk1, wk2, wk3, wk4 and wk5, respectively. During the entire experimental period, TMR was provided to the animals twice a day (0800 and 1700). In addition, animals had free access to drinking water and mineral blocks throughout the entire experimental period. The individual feed intake was recorded daily by weighing the offered TMR and the ort in the next morning before feeding. The ewes were weighed weekly on the last day of each experimental week. During the entire experimental period, blood samples were collected weekly from the jugular vein using heparinized vacuum tubes (6 mL) at 0730 (before feeding). All blood samples were kept in wet ice and then centrifuged at 3,500 × g for 15 min. The plasma was then aliquoted (1.5 mL) and stored at -20°C. The plasma concentration of glucose, urea, creatinine, triglyceride, cholesterol, albumin, low density lipoprotein-cholesterol (LDL-C), high density lipoprotein–cholesterol (HDL-C), as well as the plasma activity of lactate dehydrogenase (LDH), glutamate pyruvate transaminase (GPT), and glutamic oxaloacetic transaminase (GOT) were determined using commercial kits (Pars Azmoun, Karaj, Iran), and NEFA and BHBA were measured by a RANDOX (Randox LTD, UK) commercial kit, and an automated analyzer (Mindray, B850, China), following manufacture’s instructions. The concentration of very-low-density lipoprotein (VLDL) was determined using the following equation: VLDL (mg/dl) = TG × 0.20. The data was tested for normal distribution using the UNIVARIATE procedure of SAS (SAS Institute Inc., Cary, NC, USA, 2002-2008, Release 9.2). The data was evaluated using the MIXED procedure of SAS. The model included treatment (control and feed restriction), time (from wk 1 to wk 5), and the interaction (treatment × time) as fixed effects. The individual ewe was set as a repeated subject. Concentrations of metabolites were considered dependent variables. Significant differences were considered significant if P<0.05, and a tendency if 0.05 <P <0.10. Results are presented as means ± SEM. Results and discussion: Obtained results showed that feed restriction reduced dry matter intake in the restriction group (P<0.001). Different feed restriction percentage affected BW (P<0.01), and the lowest was related to the wk 2 in the restriction group (P<0.05). Among blood metabolites, plasma glucose, NEFA, and BHBA concentration tended to increase in the restriction group (P= 0.07). Plasma creatinine concentration was not affected by feed treatment yet the sampling times had significant effect on the same parameter in the restriction group (P<0.05). The other plasma metabolites were not affected by the feed restriction and sampling times except the LDL concentration at wk 4 in the restriction group (P<0.05). Conclusion: In conclusion, feed scarcity in tropical regions could affect body weight in the non-pregnant ewes. Per our observation, fat-tail tissue could also be considered as an energy source in these types of breeds, specially during the pregnancy and feed scarcity since blood metabolites were only insignificanly affetected.
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