نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم دامی، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان،
2 گروه علوم دامی، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان. ایران
3 گروه علوم دامی، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران.
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
In this study, 12 dairy cows (milk =51±3kg/d) were used in a replicated 3x3 Latin square design with 3 experimental periods of 28 d (21 d for adaptation and 7 d for data collection) assigned to 3 experimental diets containing wheat straw as fine (Xgm=6.9mm, grounded by forage chopper), medium (Xgm=13.3mm, chopped by feed Mixer) and mixture (50:50) of medium (in TMR) and long (top dress) straw (Xgm=22.1mm; long). By increasing particle size of straw, sorting activity against long and in favor of fine were linearly increased. Cows fed fine straw consumed about 34% of their total diet within the first 4 hours after feeding, but cows fed medium or long straws consumed 40 and 41% of their diets, respectively. Total feed intake (24 h) was similar across the diets, but NDF intake was greater in cows fed fine straw than others. Eating time increased (from 338 to 368 min/d), but eating rate and rumination time (from 535 to 504 min/d) decreased with increasing particle size of straw. Nutrient digestibility was linearly decreased as a result of increasing particle size of straw. Milk production (47.2kg), FCM (41.2kg), milk fat (2.78%), protein (2.8%), feed efficiency (1.76) and rumen pH (6.3) did not differ across the diets. Overall, increasing particle size of straw increased initial feed consumption after delivery (within 4 hours), eating rate, sorting activity. Therefore, feeding fine straw (6.9 mm) in high concentrate diet resulted in more uniform consumption of particle and a better supply of forage fiber.
کلیدواژه‌ها [English]
Extended Abstract
Introduction
Iran is located in the arid and semi-arid geographical region of the world. The proportion of pasture fodder production is limited and most of the agricultural lands is devoted to cereal grain production (about 62%, about 9.5 million hectares) as compared to the rest of the world. Therefore, it can be concluded that cereal straw is the most important fiber source available for livestock animal production. Cereal straw is a poor source of energy (ME=1.65 Mcal/kg), protein (3.7%) and also micronutrients such as minerals and vitamins, but contains high amount of neutral detergent fibers (NDF = 76.9). Therefore, cereal straw can meet the effective fiber requirement of livestock animals if the diet is balanced for energy and protein and straw is well processed (particle size and uniformity). Our research indicated that feeding straw based on undigested fiber (uNDF), as compared to conventional forage, resulted in a similar lactational performance in high-producing dairy cows (>40 kg milk/d). The physical effective NDF (peNDF) affect chewing (eating and rumination) and subsequently the secretion of saliva, rumen pH and fermentation, and milk fat. In fact, forage sources are more expensive of nutrients (except for fiber) than grains. This issue, together with the high nutritional requirement of lactating cows, has led to the minimum feeding of forage in dairy farm industry and diet containing straw. Feeding high concentrate diets with a high eating and fermentation rate can predispose the cows to sub-acute acidosis, which reduces milk fat, feed efficiency and performance. Increasing the particle size of straw, in particular high concentrate diets, may improve chewing activity and saliva secretion and promote rumen pH and health of animal. However, cows usually sorted against long forage particles and in favor of fine particles containing concentrate components. Thus, increasing straw particle size may compromise the effect of particle size in high concentrate diets on rumen and performance. Three forms of straw are available for feeding straw as long (intact), chopped with feed mixer (medium), and ground by harvester thresher (fine). The aim of this study was to investigate the particle size of straw in high-concentrate rations on chewing activity, feeding sorting and behavior, digestibility and performance of dairy cows.
Materials and Methods
Twelve lactating Holstein cows (days in milk 114 ± 11.8, milk production 48.7 ± 3.2, body weight 600 ± 18 kg, and body condition score 2.64 ± 0.26) were assigned in a replicated Latin squares 3 × 3 with 3 experimental diets and 3 periods. Each period was consisted 28 days, with the first 21 days for adaptation and next 7 days for sampling and data collection. All experimental diets contained a forage: concentrate of 32:68 (based on DM), 10% wheat straw, 12% corn silage and 10% alfalfa hay. Wheat straw was provided in 3 particle sizes namely as short, medium and long. Fine wheat straw was chopped by a forage chopper with a pore size of 10 mm, and medium wheat straw was chopped by a commercial TMR feed mixer. In treatment 3, half of wheat straw was included in the diet as treatment 2 and the other part as long form (without chopping). The geometric mean of particle size for fine, medium and long straw was 6.90, 13.3 and 22.1 mm, respectively. Voluntary feed intake (10% orts) and daily milk production were measured and analyzed for the 7 last days of each period. The sorting index was calculated at 4 and 24 hours post feeding using Penn State Particle Separator (PSPS). Nutrient total tract digestibility, chewing time and eating patterns, blood metabolites, and rumen pH were measured once in each period.
Results and Discussion
Geometric mean particle size was 9.52, 4.36, 6.9, 13.3, and 22.1 mm for corn silage, alfalfa hay, fine straw, medium straw, and long straw, respectively. The highest proportion of TMR particles on 19 mm was for long straw (72.3%), while that of on 8 mm screens was for fine straw (53.8%). The dietary geometric mean particle size was 3.38, 3.68 and 4.29 mm for fine, medium and long diets, respectively. Milk fat: protein was 0.99, 0.96 and 0.96 for fine, medium and long diet, respectively, indicating cows suffers from milk fat depression and a sign of sub-acute ruminal acidosis. The voluntary DM intake (24 h) was the same among the treatments (27.0 kg/d), but intake, after feed delivery within 4 h, was higher for long diet (41% of total intake) than for fine diet (34% of total intake). This was likely related to higher eating rate and sorting behavior that occurred for long diet. After 4 h of feed delivery, the sorting activity of TMR particle retained on 19 mm was 107% for fine diet and 74.6% and 44.8% for medium and long diets, respectively. On the contrary, sorting activity of TMR particles <1.18 mm (pan) was 107% for fine and 114% and 123% for medium and long diets, respectively. After 24 h, sorting activity was 93, 100, 100 and 101% for particle retained on <1.18 mm, 1.18-8 mm, 8-19 mm and >19 mm for fine diet, but 83, 98, 102 and 104% for particle retained on <1.18 mm, 1.18-8 mm, 8-19 mm and >19 mm for long diet. These results indicated a more uniform intake for fine diet than long diet during the day. Eating time enhanced (from 338 to 367 min/d), but eating rate (kg/min) and ruminating time (from 535 to 504 min/d) decreased with increasing the particle size of straw in the diet. Meal’s frequency and length, and total chewing were unaffected by the experimental treatments. Milk production (47.2 kg), FCM (41.2 kg), milk fat (2.78 %), protein (2.88 %), lactose (4.66%) and feed efficiency (1.76) did not differ across the diets. The level of blood urea-N increased (from 18.3 to 20.6 mg/dL) with the increasing straw particle size. The ruminal pH in cows fed fine, medium and long straw was 6.34, 6.38 and 6.19, respectively, and not affected by experimental treatments. DM and NDF digestibility was linearly reduced from 73.5 to 68.0%, and from 52.4 to 43.8%, respectively, as a result of increasing the particle size straw.
Conclusion
Due to high fiber and low palatability of straw, the inclusion of straw in the TMR diet of lactating cows may cause sorting resulting in high intake of rapidly fermentable carbohydrate and less consumption of forage fiber. This, in turn, may provoke several aspects of health and production such as disruption of rumen function, reduction of microbial activity and digestion, lameness problems, and reproductive performance. In this research, reduction of particle size of straw in the diet, from 22.1 to 6.90 mm, resulted in similar intake of all diet particles and consequently promote rumination time, nutrient digestibility and reduced BUN level, but did not affect milk production. Thus, feeding straw chopped using threshing machine as fine could be a better choice for feeding in TMR than straw chopped by feed mixers or feeding long straw.
Author Contributions
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All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
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The authors would like to thank all participants of the present study.
The study was approved by the Ethics Committee of the University of ABCD (Ethical code: IR.UT.RES.2024.500). The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
The author declares no conflict of interest.
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