| Stocking density has critical implications for broiler welfare. In order to expose the nutrient requirement of broiler chickens with different density allowances in a sex dependent fashion,4trials were conducted in this comprehensive study.In trial1, the effects of stocking density, sex and dietary metabolic energy (ME) concentration on the growth performance, footpad burns, and leg weakness were investigated.876male and1020female one day-old chicks were respectively placed into48pens to simulate final stocking density of26(10males or12females) and42(16males or18females) kg of BW/m2floor space. Two series of experimental diets with a150Kcal/kg difference in ME concentration (2800,2900and3000or2950,3050and3150Kcal ME/kg diet) were compared in a3-phase feeding program. High stocking density significantly (P<0.01) decreased average day gain (ADG) and feed to gain ratio (F/G). At high stocking density, chickens consumed less (P<0.05) feed by35d of age, thereafter the reverse was true (P<0.0001). Male chickens had significantly (P<0.001) higher average day feed intake (ADFI), ADG, and F/G compared with females. Stocking density and sex had a significant interaction for ADG and F/G By35d of age, ADG of male broilers was more severely affected by high stocking density. In contrast, females were more severely affected in ADG and F/G by high stocking density from36to42d of age. There was no interaction (P>0.05) between dietary ME level and stocking density or sex. Stocking density had no significant influence on breast, thigh or abdominal fat yield. Female broilers had significantly (P<0.01) higher breast yield and abdominal fat content. Male broilers and high stocking density had higher footpad burn and gait scores. Low ME diet increased footpad burn score rather than gait score. The result indicated that stocking density had more severe effect on the growth of male broilers before35d of age. Female broilers need more space than males at similar body weight/m2around marketing age. The incidence and severity of leg weakness are associated with sex, diet and stocking density. The result suggests that stress response should be responsible at least partially for the deteriorated performance by high stocking density.In trial2, the effects of stocking density, sex and dietary lysine concentration on growth performance, carcass characteristics, footpad burns, and leg weakness of broilers were investigated.1314male and1530female days old chicks were respectively placed into72pens to simulate final stocking density treatments of26(LSD,10males or12females/m2) and42(HSD,16males or18 females/m2) kg of BW/m2floor space. Three series of experimental diets with a20%difference in lysine concentration (120%,100%, and80%of NRC recommendation) were compared in a3-phase feeding program. HSD treatment significantly decreased ADG and F/G (P<0.01). HSD chickens consumed less feed by35d of age, thereafter the reverse was true (P<0.01). Male chickens had significantly higher ADFI, ADG, F/G compared with females (P<0.01). Stocking density and sex had a significant interaction for ADG and F/G(P<0.05). By35d of age, the ADG of male broilers was more severely affected by HSD. In contrast, females were more severely affected in BW gain and F/G by HSD from36to42d of age. The breast muscle yield of broilers was significantly decreased by HSD (P<0.05) and low lysine diet (P<0.01). Female broilers had significantly (P<0.01) higher breast muscle yield and abdominal fat content. Male broilers and HSD treatment had high footpad burn and gait scores (P<0.01). These results suggest that the lysine requirement of broilers is not altered by stocking density, and the deteriorated effect of high stocking density is sex and age dependent.In trial3, the effects of stocking density, sex and dietary vitamin D3concentration on live performance, leg health and litter quality were investigated.1314male and1530female day-old chicks were respectively placed into36pens to simulate final stocking density treatments of26(LSD,10males or12females/m2) and42(HSD,16males or18females/m2) kg of BW/m2floor space. Three series of experimental diets with a2500IU/kg difference in vitamin D3concentration (500,3000and5500IU/kg) were compared in a3-phase feeding program. Results showed that HSD significantly (P<0.05) decreased tibial mineral deposition, while increasing gait and footpad burn scores. Increasing dietary vitamin D3had no influence on growth performance, tibial ash, Ca and P, gait and footpad burn scores, and litter moisture (P>0.05). The interaction of stocking density, dietary vitamin D3, and sex was significant on plasma P concentrations (P<0.01). These results suggest that HSD inhibits tibial development, impairs walking ability, and aggravates footpad burn. A phosphorus-adequate diet used in the present study likely explains the poor result of increasing dietary vitamin D3. In fact, vitamin D3improves the growth of broilers by increasing phytate phosphorus utilization, so its positive effect on performance is exerted almost exclusively in phosphorus-deficient diets.In trial4, the effects of stocking density, sex and dietary calcium and phosphorus concentration on growth performance, tibial parameters, litter quality, footpad burns, and leg weakness of broilers were investigated,2628male and3060female one day-old chicks were respectively placed into144pens to simulate final stocking density treatments of26(LSD,10males or12females/m2) and42(HSD,16males or18females/m2) kg of BW/m2floor space. Six series of experimental diets with a25%difference in calcium and phosphorus concentration [(NCa, NP),(Ca+25%, NP),(Ca+50%, NP),(Ca-25%, NP-25%),(Ca+25%, NP+25%) and (Ca+50%, NP+50%)] were compared in a3-phase feeding program. Results showed that HSD aggravated leg weakness, increased litter moisture, but didn’t affect tibial ash, calcium and phosphorus content. Dietary calcium and phosphorus level had a significant influence on growth performance, tibial ash and phosphorus content, but not on gait and footpad burn scores. Stocking density and dietary calcium and phosphorus level had a significant interaction for gait and footpad burn scores. These results suggest that dietary calcium and phosphorus may alleviate the negative effect of high stocking density to some extent.In trial5, the effects of stocking density, sex and dietary biotin levels on the growth performance, leg health, and litter quality were investigated.1752male and2040female day-old chicks were respectively placed into48pens to simulate final stocking density of26(10males or12females) and42(16males or18females) kg of BW/m2floor space. Four series of experimental diets with a0.20mg/kg difference in biotin concentration (0,0.20,0.40or0.60mg/kg diet) were compared in a3-phase feeding program. High dietary levels of biotin had no influence on growth performance and carcass characteristics (P>0.05). Biotin and sex had a significant interaction for carcass and liver yields (P<0.05). The interaction of stocking density, dietary biotin, and sex was significant on abdominal fat content (P<0.05). High dietary concentrations of biotin did not affect litter moisture, and gait, footpad and hock burn scores, and had no interaction with stocking density (P>0.05). These results indicate that the growth response to dietary biotin differs between male and female chickens. High levels of biotin are favorable for lower fatness in broiler chickens reared at low density. The effect of increasing dietary biotin on leg health is dependent on the condition of the litter. It is impossible that high inclusion rates of supplementary biotin may contribute to the healing of leg weakness if litter moisture is greater than40%.These results show that HSD significant reduced ADG and F/G (P<0.01), improved gait and footpad burn scores (P<0.01), had negative effect on leg health and litter moisture. Stocking density had no significant influence on breast, thigh or abdominal fat yield. Female broilers had significantly (P<0.01) higher breast yield and abdominal fat content. Male broilers had higher gait scores. HME significant reduced average ADFI, ADG, F/G (P<0.01). The breast muscle yield of broilers was significantly decreased by low lysine diet (P<0.01). ADFI (P=0.01), ADG(P<0.01) and F/G (P<0.01)were significantly decreased by low lysine diet (P<0.01). And the ADFI, ADG and F/G were also significantly decreased by high lysine diet (P<0.01). Dietary calcium and phosphorus level had a significant influence on growth performance, tibial ash and phosphorus content, but not on gait and footpad burn scores. Dietary vitamin D3had no significant influence on tibial ash and phosphorus content, Dietary vitamin D3had no significant influence on growth performance, leg health, litter moisture and plasma metabolites (P>0.05). Dietary biotin had no effect on growth performance and carcass (P>0.05), high level of biotin was contribute to the footpad burn scores and tarsal joint injury. |
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