Effect of nutritional stress on wool yield, characteristics and efficiency of feed conversion to wool

S M K Naqvi and A K Rai

Central Sheep and Wool Research Institute Avikanagar (Via: Jaipur) Rajasthan 304501

Abstract

In order to study the effect of nutritional stress on wool yield, quality and efficiency of feed conversion to wool, an experiment was conducted on Chokla and Avivastra (Exotic fine wool type Rambouillet x Indigenous Carpet wool type Chokla) animals. Three groups of 9 animals each of both the breeds were offered ad libitum, 50% and 25% of ad libitum intake of feed (50% concentrate mix + 50% ground cowpea hay), individually for 16 weeks period. Chokla animals produced 54.9, 36.9 and 36.5% more wool with 114.2, 84.2 and 72.6% greater efficiency in converting feed to wool in ad libitum, 50 and 25% of ad libitum intake treatments, in comparision to Avivastra animals. Efficiency of feed conversion to wool increased with descending level of intake in both the breeds. Fleece weight indices at three levels of feeding remained similar in Avivastra animals but changed significantly in Chokla animals. Wool fibre of Avivastra animals was finer in diameter, shorter in length and possessed more crimps/cm than the fibres of Chokla animals. The staple length and fibre diameter reduced while crimps/cm of fibre increased due to the effect of lower nutrition level.

Key words: Nutritional stress, wool yield, wool characteristics, feed efficiency

Introduction

Grazing animals in arid and semi-arid regions are generally subjected to periods of undernutrition during extreme hot environment due to non availability of feed and poor pasture conditions, which in turn results in low productivity. It is important for a successful breeding programme to select the superior animals accurately, keeping in view genetic x environment interactions. The main components affecting efficiency of wool production are intake, nutritive value of feed, body weight and season (Butler and Maxwell 1984). Genetic variation is generally maintained in wool production and efficiency (Daly and Carter 1965; Dunlop et al 1966). The genetic potential of higher yielding animals are exhibited fully only when adequate feed is available (Williams 1966).

The experiment was conducted to explore the effect of ad libitum and restricted feeding on the quality and quantity of wool yield, and efficiency of feed conversion to wool in Chokla and Avivastra sheep.

Materials and methods

The study was conducted on twenty-seven (27) males of 12-14 months of age, each of Chokla and Avivastra breed. The animals of each breed after shearing were divided equally into three groups and placed separately under a shed. Individuall feeding was practised. Group AL was offered ad libitum feed during 10-16 h while groups AL50 and AL25 received only 50 and 25% of their individual ad libitum intake taken during pre-experimental period of one week. The experiment was conducted during hot months of the year. The meteorological data are presented in Table 1.

Table 1. Average dry bulb temperature, relative humidity (%) and sunshine (hrs) during the months under experiment
Month	Average dry bulb temperature (°C)		--- Relative humiditity (%) ---		Sunshine
at:	8:30 hrs	14:30 hrs	8:30 hrs	14:30 hrs	(hrs)
April	26.4	37.5	34.8	12.9	10.34
May	31.7	42.5	35.3	11.6	11.32
June	30.3	37.1	58.6	33.7	8.92
July	27.4	34.3	78.9	47.9	7.37

The animals were shorn after a period of 16 weeks and fleece yield and body weight were recorded. Wool samples were collected from mid side flank region of the body of the individual animals and processed for the quality parameters.

Composition of feed:

Feed consisted of 50% ground cowpea (Vigna Sinensis) hay and 50% concentrate mixture. The concentrate mixture consisted of barley 45 parts, ground nut cake 30, wheat bran 17, molasses 5, mineral mix 2 and common salt 1 part. The data were subjected to analysis of variance.

Results and discussion

The level of nutrition affects the wool production and efficiency (Dunlop et al 1966; Dolling and Piper 1968; Ferguson 1972). During the 16 weeks experimental period, Chokla produced 54.9, 36.9 and 36.5% more wool than Avivastra under ad libitum, 50% and 25% of ad libitum intakes respectively (Table 2). Weston (1965) found similar trend in high and low wool producing groups of Merino sheep at restricted and ad libitum feeding. The higher wool producing animals exhibit their maximum potencial with ad libitum feeding. The results of the experiment (Table 2) indicate that Chokla animals have better capacity of wool production and efficiency of conversion of feed into wool. The efficiencies of feed conversion to wool for the period under experiment were 114.2, 84.2 and 72.6% higher in Chokla under ad libitum, 50% and 25% of ad libitum intake of feed. Many researchers (Moran 1970; Saville and Rabards 1972; Robards et al 1976) have found inverse relation between efficiency and decreasing level of feeding. Efficiency of feed conversion to wool increased with decreasing level of feeding in both the breeds (P<0.01) and breed differences were also significant (P<0.01). With the decline in feed intake the increase in efficiency could be due to change in partitioning of energy between wool and meat production as also reported by Ferguson et al (1962).

Table 2. Effect of feeding level on wool production in two breeds of sheep in a hot environment (mean values and SE)
Character	Breed	---------------------------------- Feeding Level ----------------------------------
		AL	AL50	AL25
Fleece	C	1.96±0.14	1.20±0.09	0.88±0.07
yield (kg)	A	1.26±0.06	0.87±0.04	0.65±0.05
F W I	C	62.1±4.46	46.5±3.36	42.9±4.22
(g/kg)	A	27.7±1.54	25.8±1.32	24.8±1.48
Wool yield/DMI	C	22.5±1.73	23.4±1.46	33.5±3.10
(g/kg)	A	10.5±0.47	12.7±0.51	19.4±1.27
Staple length	C	6.73±0.71	4.93±0.19	3.80±0.40
(cm)	A	3.66±0.56	3.16±0.24	2.35±0.24
Crimp/cm	C	1.07±0.01	1.56±0.28	1.88±0.39
	A	1.91±0.52	2.43±0.62	2.02±1.05
Fibre diameter	C	30.43±3.31	25.58±1.43	25.12±1.26
(µ)	A	25.23±2.33	21.88±0.87	21.58±0.87
Medullation	C	21.17±8.17	15.05±9.33	12.84±6.64
(%)	A	11.99±7.44	6.72±2.51	6.36±4.51

Fleece yield in relation to body weight (Fleece Weight Index - FWI) did not change considerably in Avivastra animals. It is indicating that change in fleece yield is proportional to the loss of body weight at 50% and 25% levels of feeding. In Chokla animals FWI was reduced significantly (P<0.01) at 50% and 25% level. Thus there was considerable loss of fleece per unit body weight during feed restriction. Although during ad lib feeding Chokla animals exhibited full potential for wool production, however, this breed had considerable loss of potential of wool production than Avivastra during feed restriction; it may be due to the fact that the animal diverts the energy for other vital functions of the body. But it is important to note that FWI in Chokla animals remained significantly (P<0.01) higher than Avivastra animals at all three levels of feeding.

Table 3: Summary of ANOVA for wool production in two breeds of sheep at different feeding levels
	------------------------ Source of Variation ------------------------
	Treatment(T)	Breed(B)	(T x B)	Error
Degrees of freedom	2	1	2	48
Mean sums of squares
- Fleece yield	3.3608**	2.3663**	0.262*	0.0622
- FWI	611.87**	8037.4**	345.1*	83.706
- Wool yield/DMI	515.90**	2031.4**	13.25	25.243
- Staple length	20.273	59.346**	3.313**	1.6951
- Crimps/cm	4.1509	12.184*	0.123	2.9411
- Fibre diameter	111.07	232.13**	3.773	32.243
- Medullation	248.41	863.28	8.576	420.10

** Significant at 1% level * Significant at 5% level

Wool fibres of Avivastra animals were finer in diameter, shorter in length and possessed more crimps/cm than fibres of Chokla animals in all the three feed regimens. The wool fibres became fine at low level of intake in both the genotypes (P<0.05), and the breed differences were significant (P<0.05). This fineness of the wool under feed restriction may be attributed tho hunger fineness. Feeding levels affected the staple length in both the breeds; the percent reduction in staple length was comparatively higher in Chokla than Avivastra animals.

It may be concluded that low level of feeding at 50% and 25% of ad libitum intake reduced the fleece yield and increased the efficiency of conversion of feed to wool.

Staple length and diameter of fibre was reduced at low level of feeding while crimps/cm increased. Chokla animals possessed high potential of wool production and the potential is exhibited at higher level of feeding, while in Avivastra animals the capacity of wool production per unit body weight did not increase considerably with increasing level of feeding.

References

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