نوع مقاله : مقاله پژوهشی
نویسندگان
گروه علوم دامی، دانشکده کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The aim of this study was to investigate the growth performance, water consuming pattern, digestibility, and carcass traits of Lori-Bakhtiari (LORI) and Romanov-Lori-Bakhtiari (CROSSbred) lambs under water restriction conditions. Twenty lambs (10 heads per genotype) with an average weight of 31±2.5 and an age of 8±2 months were used in four treatments with 5 replications in each in a completely randomized design with 2×2 factorial. Water-restricted (WR) lambs had free access to water for only one hour a day. All lambs were slaughtered after six weeks. Feed intake, daily weight gain and final weight were not affected by genotype and access to water, while water intake (p=0.001) and water to feed ratio (p=0.02) were significantly dropped with water restriction. Water-restricted lambs consumed almost 90 percent of their water intake in the first five minutes. Nutrients digestibility was not affected by the treatments, but the amount of fecal dry matter was significantly high in water restricted groups (p=0.03). Carcass weight and yield were not affected by the treatments, but the percentage and weight of tails in the CROSSbred lambs were lower (p≤0.0001), but part of this decrease was compensated by higher fat thickness (p=0.05) and visceral fat (p=0.03). The overall results of this study showed that genotype and water restriction did not significantly affect growth performance, so CROSSbred lambs can be used in water restricted area.
کلیدواژهها [English]
Extended Abstract
Introduction
The increase in the world population has led to a significant increase in the need to produce animal proteins. However, the low production rate of fat-tailed native animals and the lack of water resources are important factors that make production in hot and dry areas more difficult. Crossbreeding with thin-tailed animal which have high genetic value for production and reproduction, and water consumption at certain times of the day probably can improve the situation.
Material and methods
20 healthy sheep with 8±2 months age and average weight of 31.6±2.5, which were equally from Lori-Bakhtiari (LORI) and crossbred of Lori-Bakhtiari and Romanov (CROSSbred), was used in four treatments and five repetitions for Each treatment in this study based on a completely randomized design in a 2x2 factorial format (two levels for water and two levels of genotype). Half of the animals had free access to water, while the other half had free access to water only one hour a day. The experimental diet consisted of 56% forage and 44% concentrate. After 14 days of adaptation to the solitary environmental conditions, the animals were exposed to the treatments for 42 days and were killed at the end of the period. Feed and water intake measured daily, and water intake in water restricted group monitored in 5, 20, 40, and 60 minutes. The hot carcass weight of the lambs was recorded, and then, according to the standard method, the lambs were divided into neck, head, breast, leg and and tail pieces and the weight and its ratio to the final weight was measured. In the last week, animal feces were collected and apparent digestibility was measured by acid-insoluble ash. The data was analyzed with MIXED procedure for repeated data and GLM procedure for data Non-repetitive tests with SAS 9/2 version software.
Results and discussion
This study started in the middle of summer and the average temperature-humidity index reached from 27 to 21 during the test period. Dry matter intake, Average daily gain, total weight gain, final weight and feed efficiency were not affected by experimental treatments. The amount of water intake (4.28 versus 3.35 liters per day, p = 0.001) and water to feed ratio (3.40 vs. 2.84, p = 0.02) was significantly higher in treatments with free access to water, but not affected by genotypes. LORI and crossbred lambs in water restriction groups consumed more than 88 and 93% of the water consumed in one hour in the first five minutes, and the average consumption during 5-20, 20-40 and 40-60 minutes in both genotypes was approximately between 1-4 percent. Fecal dry matter increased in both genotypes in response to water limitation (32.13 vs. 36.72 percent, P = 0.03), while the digestibility of different materials was not affected either by genotype nor water restriction. Water restriction had no significant effect on none of carcass traits, but genotype affect some of them. Carcass weight, carcass yield and weight of the carcass parts was not affected by the genotype, but the ratio of all carcass parts to the cacass weight weight was significantly higher in CROSSbred lambs (p≥0.03). In addition to, internal (0.75 vs. 0.33 kg, p=0.01) and total fat (2.08 vs. 1.45 kg, p=0.006) weight also was higher in CROSSbred lambs, while fat-tail weight (1.75 vs. 0.29kg, p= 0.0002) was higher in LORI genotypes.
Conclusion
The results obtained from this study showed that water restriction in time (not amount) per day had no effect on performance indicators and carcasses, and therefore it can be used in environments with limited access to water. On the other hand, due to the fact that almost 90% of the water consumed is consumed within five minutes, the time of receiving water can be considered even less. No difference in growth performance was observed between different genotypes, so due to less carcass fat and lower generation distance, it could be a better option for keeping in the farm.
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