Effects of dietary copper on growth performance, nutrient digestibility and fiber characteristics in cashmere goats during the cashmere slow-growing period

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Abstract

Thirty-six 2.5-year-old wether Inner Mongolian White Cashmere Goats (IMWG) (BW = 42.7 ± 3.44 kg) were used to determine the effects of dietary copper (Cu) concentration on growth performance, nutrient digestibility and fiber characteristics during the cashmere slow-growing period. Wethers were stratified by weight and randomly assigned to four dietary treatments, which included a control diet containing 5.60 mg Cu/kg DM, the control diet supplied, respectively, with 10, 20 and 30 mg Cu/kg DM (total dietary Cu level of 5.60, 15.6, 25.6 and 35.6 mg/kg DM). The experiment lasted 50 days including a 10-day preliminary trial and 10-day metabolism trial. Average daily feed intake (ADFI) did not differ among treatment groups (P > 0.05), except that the supplement providing 30 mg Cu/kg DM decreased average daily gain and gain efficiency (P < 0.05). Copper supplementation had no influence on digestibility of DM, CP and ADF (P > 0.05), however, NDF digestibility of the treatment group supplemented with 30 mg Cu/kg DM was lower compared with that of other groups (P < 0.05). Length and growth rate of cashmere fiber were higher in the treatment group supplemented with 20 mg Cu/kg DM compared with other groups (P < 0.05), but cashmere diameter was not affected by Cu supplementation (P > 0.05). In conclusion, supplementation of Cu at the levels of 10, 20 and 30 mg/kg DM to the basal diet containing 5.60 mg Cu/kg DM had no influence on ADFI or nutrient digestibility of DM, CP and ADF in cashmere goats, while 30 mg Cu/kg DM supplementation had a negative effect on growth performance and NDF digestibility. However, 20 mg Cu/kg DM supplementation of the basal diet enhanced cashmere growth. Hence, the appropriate supplemental level during the cashmere slow-growing period is deemed to be 20 mg Cu/kg DM (total dietary Cu level of 25.6 mg/kg DM).

Introduction

Copper (Cu) is an essential element required by sheep and other animals for a number of biochemical functions with deficiency and toxicity occurring frequently in many parts of the world (Davis and Mertz, 1987). Cu is an essential mineral element in ruminants that produce wool. Sheep suffering from Cu deficiency have been found to produce “steely” or “stringy” wool, which is lacking in crimp, tensile strength, affinity for dyes, and elasticity. Depigmentation of the wool has been noted as a sign of severe deficiency (NRC, 1985). Cu deficiency has also been reported in dairy and range goats (Ramirez et al., 2004, Khan et al., 2007). China is the largest producer of cashmere with 80 million goats producing 163.950 million kg of fiber, accounting for 50% of the world's total production in 2006. Most of the fiber is harvested from the Inner Mongolian White Cashmere Goat (IMWG) and the Liao Ning White Cashmere goat breeds. Nutritional Cu requirements of goats, sheep, and beef cattle are 8–10 mg/kg DM (NRC, 1981), 7–11 mg/kg DM (NRC, 1985), and 10 mg/kg DM (NRC, 1996), respectively. Species differ in susceptibility to Cu overload, and it was indicated that sheep are more sensitive to high Cu supplementation than cattle and goats (Underwood and Suttle, 1999). NRC (2007) recommended increasing the Cu requirements of lactating goats to 15 mg/kg DM, mature goats and bucks to 20 mg/kg DM, and growing goats to 25 mg/kg DM. The current recommended Cu levels for cashmere goats are based on observations recorded several decades ago (NRC, 1981). However, both livestock performance and feeding regimes have changed considerably. In addition, requirements for nutrition differ for cashmere goats depending on changing nutritional conditions due to season and depending on the seasonal nature of cashmere production (the fast-growing period from August to November, the slow-growing period from December to February, and then the non-growing period from March to July).

Most research on Cu supplementation has been generated in cattle with results indicating that Cu supplementation may affect animal performance (Ward and Spears, 1997, Engle and Spears, 2000a) and nutrient digestion (Essig et al., 1972, Reddy and Mahadevan, 1976, Saxena and Ranjhan, 1978), but the results are inconsistent. Limited research has evaluated the effects of Cu supplementation on productive performance in meat goats (Luginbuhl et al., 2000, Solaiman et al., 2001, Solaiman et al., 2006, Solaiman et al., 2007). Recent research has shown that supplementation with 20 mg Cu/kg DM (basal diet containing 7.46 mg Cu/kg DM) seemed to be the optimal supplemental Cu level for nutrient digestion and cashmere growth in IMWG during the cashmere fast-growing period (Zhang et al., 2007), whereas addition of 10 mg Cu/kg DM enhanced growth performance, improved nutrient digestibility and plasma Cu status during the cashmere non-growing period (Zhang et al., 2008). We are not aware of any studies that have observed the effects of Cu supplementation on the parameters mentioned above (Zhang et al., 2007, Zhang et al., 2008) in cashmere goats during the slow-growing period. The objectives of the present study were to determine the optimal dietary Cu level required for body growth, nutrient utilization and fiber characteristics in IMWG during the cashmere slow-growing period.

Section snippets

Animals, diets and feeding

Thirty-six 2.5-year-old IMWG wethers (BW = 42.7 ± 3.44 kg) were stratified by weight and randomly assigned to the following treatments: 5.60 (control), 15.6, 25.6 and 35.6 mg Cu/kg DM which was supplied by addition of 0, 10, 20 or 30 mg Cu/kg DM to the basal diet containing 5.60 mg Cu/kg DM. All cashmere goats were introduced to the basal diet over a 5-day period, and were then fed the basal diet replaced by 30% of the experiment diets for 2 days, by 60% for 2 days, by 90% for 1 day, and finally switched

Growth performance

Effects of dietary Cu on BW, average daily feed intake (ADFI), ADG and gain efficiency of IMWG are shown in Table 2. There were no differences in initial and final BW among treatments (P > 0.05). However, supplemental 20 mg of Cu/kg of DM in the basal diet increased ADG (P < 0.05), supplemental 30 mg of Cu/kg of DM in the basal diet decreased ADG and gain efficiency (P < 0.05), and no differences were found in gain efficiency between the control and groups supplemented with 10 or 20 mg of Cu/kg of DM (P >

Discussion

Results of the present study indicated that dietary supplementation of 10 or 20 mg Cu/kg DM had no influence gain efficiency, while 30 mg Cu/kg DM supplementation impaired growth performance in IMWG during the cashmere slow-growing period. Several experiments on Cu addition in animals have been conducted, but the results are inconsistent. Mullis et al. (2003) reported that Cu supplementation at 7 or 14 mg Cu/kg DM did not affect daily gain, feed intake or gain efficiency in Angus and Simmental

Conclusion

It is concluded that addition of 20 mg Cu/kg DM to the basal diet, containing an endogenous Cu concentration of 5.60 mg/kg DM up to the inclusion levels of 25.6 mg Cu/kg DM, will enhance cashmere performance of cashmere goats. In contrast, 30 mg Cu/kg DM supplementation (the total dietary Cu level of 35.6 mg/kg DM) will reduce growth performance and fiber digestion in IMWG during the cashmere slow-growing period.

Acknowledgement

This work was supported in part by a grant from National Key Technologies R & D Program (No. 2008BADB2B05).

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      The copper requirements for lactating does (15 mg/kg DM), mature goats and bucks (20 mg/kg DM) and growing goats (25 mg/kg DM) (with both, forage and supplement) have been recommended considering normal molybdenum (1–2 mg/kg DM) and sulfur (0.15–0.25%) intakes (NRC, 2007). During the cashmere low-growing period a total dietary level of 25 mg Cu/kg DM enhanced cashmere growth (Zhang et al., 2009). These values are much higher that the recommended level of 10 mg/kg DM for beef cattle for all physiological stages (NRC, 2000).

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