Situation of hair sheep production

In the main sheep producing countries in Latin America and the Caribbean, the phenotypes and breeds of sheep are diverse and they are generally described as “Creole”, and receive different names depending on where they are located and in some cases the same breed is named in different ways, for example the Pelibuey or Tabasco breed in Mexico, in the Virgin Islands the Pelo Blanco or Saint Croix breed, in Tobago West African or Roja Africana breed are the same. In Brazil there are three breeds of hair sheep: Morada Nova, Somali Brasileño and Santa Inês. Table 1 shows the breeds of hair sheep and their distribution in Latin America. Mature weight by sex of each breed was taken from the “Breeds of Livestock” website (www.ansi.okstate.edu/breeds/) of the Animal Science Department at Oklahoma State University¹⁵. According to NRC¹⁵, in order to obtain a more precise prediction of energy requirements, it is necessary to consider mature weight of the animals, as this is associated with composition of the retained tissue depending on the percentage of mature weight of the animal, which varies among breeds and genotypes. In sheep, it has been reported that ME requirements for maintenance decrease as the animal gets older, which is related with the proportion achieved of mature weight¹⁵.

Table 1 Breeds of hair sheep and their distribution in Latin America. 

MW= Mature weight, taken from the web site: www.ansi.okstate.edu/breeds/.

Data on energy requirements for maintenance and growth of hair sheep

A literature review using the Science Direct (http://www.sciencedirect.com/), and Google Scholar (http://scholar.google.com/) search engines was conducted to create a database, and papers published in the scientific literature were obtained from journals such as: Tecnica Pecuaria en Mexico, Brazilian Journal of Animal Science, Ciência Agrotecnica, Small Ruminant Research, Semina: Ciências Agrárias and Italian Journal of Animal Science. The method by means the ME requirement for maintenance and growth was estimated is also presented in Table 2. It can be appreciated that the work carried out with hair sheep was performed with regression and comparative slaughter techniques; different to what has been done with wool sheep, since the energy requirements of these sheep has been obtained basically with calorimetric techniques^23-26. There is a need to initiate calorimetric work with hair sheep in tropical regions to validate the data obtained by regression and comparative slaughter techniques.

Table 2 Description of the database used in this review. 

Pb= Pelibuey; Ra= Rambouillet; SI= Santa Inês; MN= Morada Nova; Do= Dorper; BS= Brazilian Somali. CS= Comparative slaughter; REG1= Regression of ME intake on changes in live weight, in experiments published in the literature; REG2= Regression of ME intake on changes in live weight (with original data from the experiments).

Energy requirements and efficiency of ME utilization for maintenance (k_m)

Energy costs for maintenance represent between 60 and 80 % of total energy consumed by ruminants²⁵. Energy requirements and in particular those for maintenance (E_m), as well as the efficiency of feed utilization and the energy contained in tissues (adipose, muscular) in cattle has been a research subject during several decades^25,27. The requirement of metabolizable energy (ME) for maintenance (ME_m ), can be equated to the so-called “basal metabolism” (mostly used in human nutrition) and is defined as the amount of energy that the animal needs in order to maintain vital processes (basic functions [heart, lung, kidney, nervous, “work”] and cellular functions [fat and protein turnover; Na/K ion pump]) of the body under normal conditions. In a practical way, the ME _m could be defined as the state in which the animal does not suffer changes in its body composition^9,23. It has also been defined as the state in which ME intake (MEI) will not result in loses or gains of energy (RE) in the animal body tissues; Ferrell and Oltjen²⁸ define this unit as, ME_m= MEI at which RE= 0; or HP (heat production)= MEI.

Among the factors which influence E_m: body weight (BW), breed, sex, physiological condition, nutritional level, environmental conditions, stress, exercise, or physical activity and parasitism can be listed^9,15. The efficiency of utilization of ME_m (k_m ) represents that fraction of ME which can be converted to net energy (NE), to support maintenance requirements of the ruminant. The fraction which is no converted to NE is lost as heat increment including fermentation in the gastrointestinal tract and biochemical reactions at the cellular level²⁹. The efficiency of energy utilization of feedstuffs has an economic impact, and the best way to determine it is by means of feed conversion efficiency^27,30.

Table 3 shows estimations of ME and NE requirements for maintenance (ME_m and NE_m respectively) and Table 4 shows efficiencies of ME utilization for maintenance (k_m ) estimated in hair sheep of different breeds under tropical conditions of Latin America.

Table 3 Energy requirements for maintenance estimated in hair sheep in tropical conditions of Latin America. 

Pb= Pelibuey; Ra= Rambouillet; SI= Santa Inês; MN= Morada Nova; Do= Dorper; BS= Brazilian Somali. CV= Coeficient of variation.

Table 4 Efficiency of utilization of ME for maintenance (k_m ) in hair sheep. 

SD= Standard deviation; CV= Coefficient of variation.

It is important to point out that for the case of ewes, in the present review only two experiments were found which were related to this information^31,32 and the mean value (± standard deviation) for ME_m was 419 ± 129 kJ/kg BW^0.75. This information must be taken with reserve since it comes from a reduced number of observations. In this sense, Chávez et al³³, found that supplying 506 kJ/kg BW^0.75 to Pelibuey ewes during the first 100 d of pregnancy and 700 kJ/kg BW^0.75 during the last 50 d of pregnancy was enough for the ewes to gain weight (36 g/d approximately). Along with this, they reported that for lactation, the supply of 1,000 kJ/kg BW^0.75 was enough for the ewes to gain 4 to 20 g/d, producing 700 to 800 ml of milk and be able to sustain a weight gain by their lambs of 200 g/d.

For growing male sheep, data from nine experiments were used which involved Pelibuey^3,32, Santa Inês^4,18,20, Morada Nova^8,34, 1/2 Dorper × 1/2 Santa Inês³⁰⁾ and Brazilian Somali lambs²⁶. The mean value found in the present experiment for ME_m was 388 ± 123 kJ/kg BW^0.75; however, this data showed a relatively high coefficient of variation of 31.8 %, this variation can be attributed to differences between experiments, genotypes, and crosses, among several other factors.

In several experiments^{8,20,22,26,34} the values for ME_m (kJ/kg BW^0.75) were derived from the relation of BW/EBW and using the k_m reported by these authors. In relation to ME _m , in growing Santa Inês sheep, some authors^4,20 report a mean value for ME _m of 342 (±107) kJ /kg BW^0.75. for Morada Nova sheep^8,34 an average ME _m of 264 (±8.23) kJ/kg; for Pelibuey^3,32, a mean value of 544 (±76.4) kJ/kg. While others^26,30 reported only values available for 1/2 Dorper × 1/2 Santa Inês and Brazilian Somali lambs (Table 3).

In relation to k_m , it was found an average value of 0.70¹⁸. An average value of 0.67 was reported⁸ when estimating k_m in diets with forage proportions of 40, 55 and 70^4,7,20; in Santa Inês growing males reported a k_m value of 0.66. Recently³⁰ it was found a k_m of 0.63 in 1/2 Dorper × 1/2 Santa Inês lambs. The mean value for k_m in the present review was 0.66. In this respect, even when ME of diets of medium quality (such as those commonly used in the tropics) is utilized with a low efficiency for maintenance and gain, k_m is relatively higher compared to k_g ²⁹. Furthermore, this author reported that k_m could be considered on average as 0.60 independently of the diet. This approximates to that found in this work, where an average k_m value of 0.66 was obtained (Table 4).

Lack of information is more evident for the case of ewes, for which there are very few reports regarding determination of energy requirements in their different physiological stages (maintenance, pregnancy, lactation), being these fundamental components of the production systems. Furthermore, it is known that feeding of ewes before and after parturition has an effect on survival and growth of the offspring. It is thus necessary to continue with work focused on the determination of the nutrient requirements of hair sheep and develop a feeding system based on characteristics of the ration, breed and environmental conditions prevailing in Latin American tropics. Ration formulation with precise knowledge of the energy requirements of hair sheep and the concentration of ME (and its efficiency of utilization), of the feedstuffs available in the tropics, will have an influence on improvement in sheep production, by giving sheep the precise amount of feed that require without over or under estimating its requirements nor the energy value of feedstuffs. Ration formulation for sheep based on the precise knowledge of their requirement for maintenance and production, will contribute to reduce production costs, since there would probably be a lower waste (as heat increment) arising from ME absorbed from the GIT. Knowledge of energy requirements of hair sheep for the different physiological stages (maintenance, growth, pregnancy and lactation), is of paramount importance since these could be readily incorporated in different programs for ration formulation (CNSPS-S/SRNS) and with these, formulates rations that will satisfy the energy requirements of hair sheep kept under tropical conditions.

Energy requirements for weight gain and estimated k_g

The energy requirement for growth or weight gain (ME_g or NE_g), corresponds to the caloric value or gross energy of the protein and fat stored in the body²³. The ARC²³ mentioned that rate of growth affects protein deposition which in turn affects NE requirements. Composition of weight gain, expressed as empty body weight (EBW), is the main determinant of energy requirements for weight gain, which is estimated from energy retained in the body¹⁵. Moreover, the main factor determining the composition of gain in the mature stage, in which as the animal is closer to its adult weight, more fat (and energy) is stored in the gain.

Ferrell and Oltjen²⁸ reported that ME in the ration is used with different efficiencies depending on the type of ration (ingredients), level of intake and the physiological function for which it is being utilized by the animal. Tolkamp²⁹ reported that k_g for rations of low to medium quality (such as those of tropical forages), is expected to be low. Tedeschi et al³⁵⁾ mentioned that there are factors which may affect k_g , pointing out that ration (energy density and volatile fatty acids molar proportions) and the composition of the weight gain are the most important issues; these authors concluded that the use of a combination of chemical composition of the body and energy concentration of the ration may be a better approach for the assessment of efficiency of utilization of ME for maintenance and growth. Indeed, some authors^36,37 demonstrated that the main factor affecting k_g is the composition of gain in the EBW; even when the level of ME interferes with k_g , a ration with a high ME concentration, will induce a high fat content in the gain, therefore, the effect of the energy content of the ration is considered in the composition of the gain.

On the other hand^36,37 these same authors did not find evidence of genetic background on NE requirements for weight gain, concluding that the effect of breed or genotype on NE for gain can be attributed to the different mature weights and to the precocity of fat deposition in the different breeds of cattle. Different mature weights of breeds, may determine different degrees of maturity in animals with the same absolute weight and the same rate of gain, high energy concentrations are expected in the gain of animals of breeds with low weight at maturity compared to that of late maturity breeds. In the present review, works with Morada Nova lambs^8,21 estimated values of 13.8 to 17.9 kJ NE/g gain and 7.0 to 9.2 kJ NE/g gain respectively, in animals weighing from 15 to 30 kg. Regadas-Filho et al²² in Santa Inês growing male lambs reported values of 10.0 to 14.5 kJ NE/g gain in animals between 15 and 30 kg. Nonetheless, in Santa Inês growing male lambs found values of 6.0 to 9.0 kJ NE/g gain^7,20. Galvani et al³⁰ and Pereira et al²⁶ reported values of 9.3 to 14.7 and 9.2 to 11 kJ NE/g gain in 1/2 Dorper × 1/2 Santa Inês and Brazilian Somali lambs, respectively. Using the values described above, it was found a mean value of 8.75 to 14.06 kJ NE/g gain in hair sheep of different breeds under tropical conditions of Latin America. Table 5 shows NE requirements for daily weight gain (MJ/animal/d) of hair sheep according to live weight and expected weight gain.

Table 5 NE requirements for weight gain (MJ/sheep/d) of Santa Inés, Morada Nova, 1/2 Dorper × 1/2 Santa Inês and Brazilian Somali hair heep weighing between 15 and 45 kg. 

BW= Body weight; ADG= Average daily gain; SD= Standard deviation; CV= Coefficient of variation.

As regard to the efficiency of ME utilization for growth, it has been reported that in growing Pelibuey sheep, this value varies according to age and weight, being higher during the first stages of growth and decreasing as the animal approaches mature weight, due to a greater fat deposition in body tissues³². However, those authors also suggested that the greater demand may be due to the higher requirement of energy per unit weight gain. Table 6 shows estimations of k_g in hair sheep. The k_g reported for hair sheep ranged from 0.38⁸ to 0.48³⁸. The average k_g value obtained for the purpose of this review was 0.42 ± 0.04.

Table 6 Efficiency of utilization of ME for weight gain (k_g ) in hair sheep. 

SD= Standard deviation; CV= Coefficient of variation.

Based on the data obtained in this review regarding the energy requirement of weight gain (MJ NE/animal/d) and k_g (0.42), it was found that the energy requirements for weight gain (kJ ME/g gain) ranged from 20.8 to 33.5 (mean: 27.7). Similarly, it was reported that the mean values for the energy requirements for gain (MJ ME/animal/d) derived, were higher by 26 % than those previously reported for growing Pelibuey sheep³⁹, nonetheless, it is important to emphasize that the data of the present review and from others³⁹, average daily gain were closer of 100 g (5 % higher on average), compared to higher rates of gain.

Energy requirements of grazing sheep

In tropical regions, sheep production systems are usually mixed, where in most cases, animals (ewes mainly) are maintained grazing with or without supplementary feed. Feeding is based on the use of native and introduced grasses and shrubs; sheep farms have low production and profitability parameters and low rate of adoption of new technologies. For that reason estimation of nutrient requirement of grazing sheep must be of paramount importance. However, there are few reports of experiments where nutrient requirements of grazing sheep have been determined. In this context⁴⁰, with Rambouillet × Pelibuey sheep recently weaned of 13.5 kg grazing Buffel (Cenchrus ciliaris) grass, found an energy requirement for maintenance of 359 kJ ME/kg BW^0.75/d. On the other hand⁷ considering a k_m of 0.66, reported a ME_m of 470 kJ ME/kg, therefore NE_m was 310 kJ/kg BW^0.75. Similarly, reported that in lambs of 3 to 4 mo old (castrated males) of the Santa Inês breed of 15 to 30 kg live weight grazing buffel grass had a requirement of 18.2 kJ ME/g weight gain in lambs of 15 kg. In lambs of 20 kg, the requirement was 24 kJ, in lambs of 25 kg the requirement was 30 kJ and in animals of 30 kg it was 35 kJ. The estimated k_g value was 0.42 for all weights evaluated.

Empty body weight (EBW)

Marcondes et al³⁶ suggested that the first step in the determination of energy requirements of ruminants is the conversion of shrunk BW (SBW) to EBW. Also, some authors mention³⁰, that the energy concentration in the body has usually been expressed as a function of EBW rather than SBW because interference by the gastrointestinal content is completely eliminated. The EBW is equivalent to SBW minus the weight of the gastrointestinal contents. SBW is also defined as 96 % of full BW (kg) and defines EBW as: EBW = 0.85 × SBW (kg)^12,16,30.

Nonetheless, to determine the EBW, sheep have to be slaughtered; for this reason, regression equations have been developed to estimate EBW from BW or SBW and include this information and thus contribute to updating with the data for estimation of some parameters required by nutritional models such as SRNS in order to predict the performance of hair sheep breeds^11,32.

Based on data reported^{8,22,26,30,34,38}, a linear regression equation was fitted.

It was found that gastrointestinal fill was 10 % and the EBW was 90 % of BW in male animals. The values found in the present work as regard to BW corresponding to EBW were higher to those reported in the literature^16,32. Also it was found that the relation BW/EBW was on average 1.23 for males.

Regarding females, in adult Pelibuey ewes at different physiological stages the weight of the gastrointestinal content was approximately 19 % of SBW¹¹. Recently, (Chay-Canul, unpublished data) used a data set of 28 adult Pelibuey ewes with different BW and body condition score and when analyzed, the data conformed an equation:

The EBW corresponded to 92 % of BW. Moreover, the relation BW/EBW was on average 1.22 for ewes.

Body composition and its relationship with energy requirements

In order to estimate nutrient requirements it is important to know body composition and weight gain of sheep because these are directly related. Fernandes et al⁴¹ suggested that knowledge of body composition of the animals is of great relevance in studies of animal nutrition to determine nutrient requirements. Costa et al²¹ and Maia et al¹⁹ reported that the first step for determining nutritional requirements is to measure the body composition of the sheep, which may be obtained by direct or indirect methods. Although the direct determination of body composition by grinding and analyzing all body tissues is the most reliable method, it is expensive, time consuming, and laborious.

Sheep body composition is an important factor when determining nutritional requirements, since the body is basically composed of water, protein, fat and minerals, in proportions that vary according to breed, age, rate of growth, sex and nutrition, among others³⁴.

In Morada Nova lambs weighing 15.23 to 25.43 kg, reported that the body composition (% EBW) varied from 70.14 to 64.61 % water, 18.14 to 18.17 % crude protein, 6.7 to 12.1 % fat and 7.28 to 9.50 MJ/kg EBW⁸. Those authors also reported that the concentration of crude protein was reduced from 181.76 to 178.74 g/kg EBW when the BW of animals increased from 15 to 25 kg. Others³⁴, informed that the energy and fat contents of the EBW increased from 6.86 MJ/kg and 79.38 g/kg EBW, to 8.83 MJ/kg and 123.73 g/kg of EBW, respectively, as the BW of the animals increased from 15 to 30 kg; a quadratic effect was also observed for the concentrations of water and fat with increasing EBW and the percentage of protein showed a tendency to decrease linearly, representing a decrease of 0.10 percentage points for each kilogram increase in EBW.

In Santa Inês lambs²², reported that the energy and fat contents of the EBW of the sheep increased from 7.99 MJ/kg and 85.16 g/kg of EBW, respectively, to 11.63 MJ/kg and 221.23 g/kg, as the BW increased from 15 to 30 kg; they also observed a quadratic effect for the concentrations of water, fat, and energy with increasing EBW and informed that the percentage of crude protein showed a tendency to decrease linearly, representing a decrease of 0.12 percentage points for each kilogram increase in EBW, from 15 to 30 kg. Those authors, concluded that the net energy requirement for EBW gain increased with increasing body weight, due to a parallel increase in the quantity of fat deposited per kilogram gained. Correspondingly, some authors³⁸, found that the crude protein content of the body decreased but fat and energy body content increased as the EBW increased from 15 to 45 kg. Similar results⁷ mention that the positively DM content in the EBW from 31.15 to 35.18 and to 36.19 %. However, the crude protein content in the EBW decreased with supplementation (P<0.05). This can be explained by the higher BW gain and fat deposition with the increase in supplementation level. The energy content in the EBW ranged from 6.23 to 8.66 MJ/kg EBW. The crude protein concentration decreased from 212 to 180 g/kg EBW when the body weight increased from 15 to 30 kg. The fat contents in 15 to 30 kg BW lambs ranged from 17.3 to 103.2 g/kg EBW. These authors concluded that the protein requirement decreased and the energy requirement increased with the increase in body weight.

Galvani et al³⁰ found that fat concentration in the gain (g/kg EBW gain), increased with an increase in the BW of the lambs and that the amount of crude protein in the gain was not affected by slaughter weight. Pereira et al²⁶ with Brazilian Somali lambs, reported that the animal’s energy and EBW fat contents increased from 11.20 MJ/kg and 208.54 g/kg to 13.54 MJ/kg and 274.95 g/kg of EBW, respectively, as the BW increased from 13.0 to 28.70 kg.

Using the data obtained in the present review, the body composition of hair sheep was plotted against the EBW, and three equations were fitted to predict body composition (Figure 1). The equations fitted were:

Figure 1 Body composition of male hair sheep as a function of empty body weight (EBW).