نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه مهندسی علوم دامی، دانشکده کشاورزی، دانشگاه شهرکرد، شهرکرد، ایران.
2 گروه مهندسی علوم دامی، پردیس کشاورزی و منابع طبیعی دانشگاه تهران، دانشگاه تهران، کرج، ایران
3 گروه مهندسی علوم دامی، دانشکده کشاورزی، دانشگاه شهرکرد، شهرکرد، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Milk production in goats is affected by genetic and environmental factors. Thus having knowledge about these factors is necessary for effective management and accurate estimation of animals breeding value. Data which were collected during 7 years (2002-2009) in the Animal Breeding Research Station of Shahrekord University were used to study the influence of environmental factors on milk production and composition of Saanen goats in this research. Repeated measurements were analysed using mixed model by including year, month, type of kidding, parity and week of lactation as fixed factors and the goat effect as a random factor. The fat percentage and the milk production on the test day were significantly influenced by all of mentioned factors (p<0.05). Month of kidding had no significant influence on protein and total-solid-non fat content (p>0. 05), and the parity had significant influence on all milk production traits (p<0.01). The highest daily milk production was belonged to goats with kidding months of February (2.59 ± 0.17 kg), twining goats (2.06 ± 0.16 kg) and in the fifth parity (2.54 ± 0.22 kg). As lactation progressed, the fat, lactose and total fat content increased. Milk protein content were decreased from early to the middle of lactation stage. Attention to non-genetic factors is necessary for efficient seleciom , establishing appropriate management practices, and ensuring stable milk production in lactating Saanen goats.
کلیدواژه‌ها [English]
Extended Abstract
Introduction
Goat milk is a special food that is full of vitamins, minerals and high-quality proteins. There are an estimated 16 million goats of different breeds in Iran, and due to labor-intensive production methods, their superior characteristics have not been widely researched or studied thoroughly. Iran received its first import of the Saanen breed in the early 1960s. Although this goat breed is currently bred in Iran under different climatic conditions, little is known about its milk production, quality and composition, as well as the genetic and non-genetic factors that influence goat performance in Iran. The objectives of the current study were to evaluate the quantity and quality of Saanen goat milk production under the Shahrekord climate over the course of the milking season, as well as the effects of non-genetic variables such as year and month of breeding, litter size, parity and milking period.
Materials And Methods
Milk records of Saanen goats which were collected between 2002 and 2009 in the Animal Breeding Research Station of Shahrekord University were used in this research. The management of the herd was semi-intensive, so that the herd is kept on the station and fed in door from early December to early May and grazed on pasture for the rest of year. The goats ration was adjusted based on age, sex, stage of pregnancy and lactation. Diet composition was set at 40% concentrate (including barley, wheat bran, sugar beet pomace and cotton seed meal) and 60% alfalfa. In the first three years, only the amount of goat milk was recorded. After weighing each goat's milk, a 60 ml fresh milk sample was collected to measure the content of fat, protein, lactose, and fat-free solids. The milk samples were analyzed using the Lactostar device manufactured by Funk Gerber in Germany and a special program for goat milk. Fleischman's method was used to calculate total milk production in a lactation period (Barillet et al., 1999). Data analysis of variance was performed using SAS software (version 9.4). The data were analyzed using a mixed statistical model with repeated measures with fixed factors as year and month of kidding, litter size, parity, days in milk and random effect of goat. Comparison of means were done using the Tukey test.
Results
The effect of the kidding year had a significant influence on all characteristics of daily milk production, milk composition and total milk production (p<0.01). The month or season of kidding caused a significant change (p<0.01) in daily milk production and fat percentage. The influence litter size on protein percent and total milk production was not significant. Parity had a noticeable and significant effect (p<0.01) on all characteristics of daily milk production, total milk production and its composition. The average daily milk production of goats was lowest in the first and seventh parity (1.23 and 1.84 kg, respectively) and highest belonged to the fifth parity (2.54 kg). Goats of the fourth parity (580 kg) had the highest total milk production. The influence of lactation week had a significant influence (p<0.001) on the characteristics of daily milk production and milk composition.
Conclusion
In general, the results of the present study showed that goats that gave birth in the winter months have more milk production and a longer lactation period. Goats that reach peak milk production late in the fifth parity were likely to have been low in age and weight at first mating. Due to the inconsistent weather and management conditions, the influence of the year and the lactation phase on milk production and its components was significant. In addition, when comparing milk production, it is recommended to take into account the number of kids born as a correction factor.
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