Feeding efficiency of lambs finished in feedlot and fed alfalfa hay and/or black oat grains

[Eficiência alimentar de cordeiros terminados em confinamento e alimentados com feno de alfafa e/ou grãos de aveia preta]

ABSTRACT

The aim of this research was to evaluate the feed efficiency of lambs fed diets composed of alfalfa hay and/or black oat grains in a feedlot. 30 weaned lambs were distributed in a 3x2 factorial scheme (three diets and two sexes). The experimental diets were roughage only (ROU), roughage (50%) and concentrate (50%) (RCO) and concentrate only (CON). The slaughter criterion used was body condition score. There was no interaction between diet and sex. The lambs in the ROU treatment consumed more dry matter (DM) and consequently more nutrients. The RCO lambs consumed intermediate values, and the CON animals consumed less DM and nutrients. Males consumed more DM. Lambs from the ROU treatment had a higher final body weight compared to lambs from the RCO treatment. The average daily gain was higher in the RCO lambs compared to the ROU lambs. The lambs' feed efficiency was best in the CON treatment, followed by the RCO and the ROU treatment lambs had the worst feed efficiency. Females have better feed efficiency when evaluated by bionutritional efficiency.

Keywords:
alfalfa hay; black oat grains; feedlot; Ovis aries; performance

RESUMO

O objetivo da presente pesquisa foi avaliar a eficiência alimentar de cordeiros alimentados com dietas compostas de feno de alfafa e/ou grãos de aveia preta em sistema de confinamento. Foram utilizados 30 cordeiros desmamados, distribuídos em um esquema fatorial 3x2 (três dietas e dois sexos). As dietas experimentais foram: somente o uso de volumoso (ROU); volumoso (50%) e concentrado (50%) (RCO); e somente concentrado (CON). O critério de abate utilizado foi o escore de condição corporal. Não houve interação entre dieta e sexo. Os cordeiros do tratamento ROU consumiram mais matéria seca (MS) e, consequentemente, maior consumo de nutrientes. Os cordeiros do RCO consumiram valores intermediários, e os animais do tratamento CON consumiram menos MS e nutrientes. Os machos consumiram um maior teor de MS. Cordeiros do tratamento ROU tiveram maior peso corporal final em comparação aos cordeiros do tratamento RCO. O ganho médio diário foi superior nos cordeiros do tratamento RCO em relação aos cordeiros ROU. A eficiência alimentar dos cordeiros foi melhor nos animais do tratamento CON, seguidos do RCO, e os do tratamento ROU tiveram a pior eficiência alimentar. As fêmeas têm melhor eficiência alimentar quando são avaliadas pela eficiência bionutricional.

Palavras-chave:
confinamento; desempenho; feno de alfafa; grãos de aveia preta; Ovis aries

INTRODUCTION

The use of feedlot for finishing lambs is used when there is an interest in intensifying the production system. In this sense, it is essential to use lamb, a young category that has a high growth rate (Van Der Merwe et al., 2020). This is associated with the use of quality roughage and concentrates and an adequate balance in the diet (Nascimento et al., 2020), as they are animals with high nutritional requirements (Gallo et al., 2014).

The efficiency of the lamb production system in feedlot is linked to the nutritional quality and adequately balanced diets provided. In addition, the use of concentrate-rich diets for ruminants, based on cereal grains, is advantageous, as there is greater feed efficiency (Oliveira et al., 2015; Trabi et al., 2019). Feeding lambs based on the use of cereal grains and hay is considered expensive, since the price of bulk and concentrate is highly fluctuating and affected by rainfall (Majdoub-Mathlouthi et al., 2013).

Generally, corn, soybean meal, hay and silage are used as the main ingredients in the diet of confined lambs (Nascimento et al., 2020). Our research proposal was to use black oat grains (Avena strigosa Schreb) as a source of concentrate and alfalfa hay as a source of roughage. In view of this, it is important to study feed efficiency, as these ingredients can alter the animal's intake pattern and, consequently, the lambs' performance.

The animals need to be as efficient as possible, in the sense that they have adequate food consumption and optimum animal performance. In the literature, there are several studies (Majdoub-Mathlouthi et al., 2013; Brand et al., 2017) in the sheep area that evaluate efficiency through feed conversion (kg dry matter/kg live weight) and/or feed efficiency (kg live weight/kg dry matter). Nutritional efficiency can be assessed using the multivariate biological nutritional index or bionutritional efficiency and is more effective and it considers dry matter consumption as a percentage of body weight, along with average daily gain (Mello, 2007).

Based on this, the hypothesis is that animals that eat a diet with a higher concentrate content will have better feed efficiency. Regarding the sex of the lambs, it is believed that males will have better feed efficiency. Considering the above, the aim of the research is to examine the feed efficiency of lambs (males and females) fed diets composed of alfalfa hay and/or black oat grains in a feedlot system.

MATERIAL AND METHODS

The group of animals consisted of 15 intact males and 15 females (30 lambs were used). The breed constitution was 1/2 Suffolk 1/4 Lacaune 1/8 Ile de France and 1/8 Texel. After weaning, they were identified, weighed, and distributed in a 3x2 factorial scheme (three diets and two sexes), with five repetitions. The animals were confined in individual, fully covered stalls with slatted floors, with an area of approximately 2m², equipped with drinking fountains and feeders. The experimental diets consisted of using only roughage (ROU), roughage and concentrate (RCO) and only concentrate (CON).

The roughage used was alfalfa hay (Medicago sativa L.) and the concentrate was basically black oat grains (Avena strigosa Schreb) (Table 1). Soybean meal (Glycine Max) and calcitic limestone were added to the CON diet to meet the nutritional requirements (Nutrient…, 2007) for crude protein and minerals, respectively (Table 2). Sodium bicarbonate (NaHCO3) was used to regulate rumen pH by a total of 1% of the dry matter (DM) offered. Mineral salt was provided at will in individual containers. Food was provided ad libitum at 8.30am. The amount offered was adjusted according to the surplus observed each day, which was 10% of the amount offered the previous day, to guarantee the animals' maximum voluntary consumption. The experimental period was preceded by a 12-day period for the animals to adapt to the conditions of the facilities, feeding and handling.

Table 1
Chemical composition of the feeds supplied in the planes of nutrition, expressed in DM (dry matter; %)

Variable	Alfalfa hay	Oat grain	Soybean meal	Calcitic limestone	Sodium bicarbonate
Dry matter	85.23	86.28	86.79	100	100
Organic matter	92.57	96.66	94.94	-	-
Crude protein	25.04	13.00	52.70	-	-
Neutral detergent fiber	40.31	28.79	12.40	-	-
Acid detergent fiber	30.60	14.80	10.02	-	-
Total digestible nutrients	58.47	78.65	73.00	-	-
Ether extract	3.63	4.68	2.20	-	-
LE (2)	1.31	1.80	1.66	-	-
DIVMS	86.79	79.31	98.11	-	-
Calcium (3)	1.29	0.07	0.34	37.33	-
Phosphorus (3)	0.23	0.35	0.58	0.03	-

• LE= liquid energy; DIVMS: In Vitro Digestibility of Dry Matter
• ^*
  ²⁾Value calculated according to Moe and Tyrrel (1976) - LE= (0.0245 x %TDN) - 0.12;
• ^*
  ³⁾ Tabulated value

Table 2
Proportion of ingredients and chemical composition of experimental diets

Ingredients	Diets
	ROU	RCO	CON
	Proportion of ingredients (% DM)
Alfalfa hay	100.00	48.59	0.00
Oat grain	0.00	51.41	81.32
Soybean meal	0.00	0.00	15.65
Calcitic limestone	0.00	0.00	2.03
Sodium bicarbonate	0.00	0.00	1.00
Chemical composition (%DM)
DM	85.23	85.77	86.73
OM	92.57	94.69	93.46
CP	25.04	18.81	18.81
NDF	40.31	34.35	25.37
ADF	30.6	22.43	13.60
TDN	58.47	68.91	75.38
EE	3.63	4.17	4.15
LE (1)	1.31	1.57	1.73
DIVMS	86.79	82.92	79.84
Ca(2)	1.29	0.66	0.87
P(2)	0.23	0.29	0.38

• DM: Dry Matter; OM: Organic Matter; CP: Crude Protein; NDF: Neutral Detergent Fiber; TDN: Total Digestible Nutrients; LE: Liquid Energy; EE: Ethereal Extract; DIVMS: In Vitro Digestibility of Dry Matter; Ca: Calcium; P: Phosphorus.
• ^*
  ¹⁾ Value calculated according to Moe and Tyrrel (1976) - EL = (0.0245 x %TDN) - 0.12;
• ^*
  ²⁾ Tabulated value

The lambs were weighed and assessed for body condition score (BCS). The score ranges from 1 to 5 and was assessed by trained assessors at the start of the experimental period and every 14 days. And more often when they were close to the pre-established score for slaughter (BCS: 3.0). The average daily weight gain (ADG) was obtained from the difference in body weight between the initial weigh-in and the final weigh-in, divided by the number of days they remained in the feedlot. For the slaughtering process, the animals were weighed after a 14-hour solids restriction to obtain the slaughter weight (SW).

Nutrient intake was calculated as the difference between the amount of nutrient present in the food provided and the amount in the leftovers. Every two days during the experimental phase, leftovers of the diet were collected and stored in a freezer for later analysis. At the end of the experimental period, they formed a composite sample/treatment/animal.

The food samples were pre-dried in a ventilated oven at 55°C for approximately 72 hours and then ground in a "Willey" type mill with a 1mm and 2mm sieve. The DM content of the samples was determined by drying them in an oven at 105ºC for at least 8 hours. Ash content was determined by combustion at 600ºC for 4 hours and organic matter (OM) by mass difference. The protein content was determined using the Kjeldahl method (Method 984.13; Official…, 1997).

Neutral detergent fiber (NDF) analysis was based on the procedures described by Mertens (2002) using thermostable α-amylase. The samples were weighed into polyester filter bags and treated with neutral detergent in an autoclave at 110°C for 40 minutes (Senger et al., 2008). Acid detergent fiber (ADF) concentrations were analyzed according to AOAC Method 973.18 (Official…, 1997). The ether extract (EE) content was determined using an ether reflux system (Soxtherm, Gerhardt, Germany) at 180°C for two hours. The Total Digestible Nutrient (TDN) content was determined based on the disappearance of organic matter from samples incubated for 48 hours in the rumen of a fistulated bovine. Feed conversion (FC) (average dry matter consumption in kg / average daily gain in kg) and feed efficiency (FE) (average daily gain in kg / average dry matter consumption in kg) were calculated. Efficiency was assessed using the multivariate biological nutritional index or bionutritional efficiency (BNE).

The multivariate analysis of variance - MANOVA - supplemented by Fisher's first canonical discriminant function (Mello, 2007) was used to calculate the BNE. Therefore, the variables ADG (kg/d) and CMS (kg/d) were submitted to MANOVA in a completely randomized design, disregarding the factorial arrangement, according to the statistical model:

$Y_{ijk}={\mu }_k+{\alpha }_{ik}+{\epsilon }_{ijk}$

in which, Y ijk= observed value of the k-th variable, under the i-th treatment in the j-th repetition; μk= general average of the k-th variable; αik= effect of the i-th treatment on the k-th variable; and εijk= random effect associated with observation Y ijk assuming NIID (0,σ 2 ) ; ∀ i=1, 2, . .., 6 ; ∀ j=1, 2,..., 6 and ∀ k=1, 2.

From the MANOVA, the eigenvalues were calculated by determining the characteristic roots of the equation (Harris, 2013): $\left|E^{-1}H-\lambda I\right|=0$ in which, E^-1= common inverse of the matrix of sums of squares and residual products; H= matrix of sums of squares and products for treatments; λ₁ and λ₂= eigenvalues of the matrix E^-1H ; and I= identity matrix of order p=2 .

The non-normalized eigenvector associated with the largest eigenvalue was then estimated by solving the system of equations: $\left(E^{-1}H-{\lambda }_{1}I\right)\nu =\left[00\right]\Rightarrow \left(E^{-1}H-{\lambda }_{1}I\right)\left[ab\right]=\left[00\right]$ in which, λ₁= largest eigenvalue; ν= non-normalized eigenvector associated with the largest eigenvalue; a and b= canonical coefficients; and E^-1 , H and I= as defined above.

Subsequently, the eigenvector was normalized by the solution of the linear system, according to the constraint: $l^{\prime }\frac{E}{n_e}l=1\Rightarrow \left[a\text{'}b\text{'}\right]\frac{E}{n_e}\left[a^{\prime }{b}^{\prime }\right]=1$ in which, $l$= normalized eigenvector associated with the largest eigenvalue; $l\text{'}$= transpose of the normalized eigenvector; E = matrix of sums of squares and residual products; n_e= number of degrees of freedom of the residual; a' and b'= canonical coefficients.

Next, we calculated the Fisher linear discriminant function (FLDF) or first canonical variable (VC1), defined by: $Z=a^{\prime }Y+b\text{'}X$ in which, Z = Fisher's linear discriminant function or first canonical variable; Y= animal transformation (ADG, kg/d); X=DM consumption (DM, kg/d); a' and b' as defined above. The values of this function were called the nutritional index of bionutritional efficiency - BNE (Detmann et al., 2005).

The experimental design adopted was entirely randomized in a 3×2 factorial scheme (three diets and two sexes), with 5 repetitions, according to the statistical model: $Y_{ijk}=\mu +{\alpha }_i+{\beta }_j+\alpha {\beta }_{ij}+b_1\left(X_{ijk}-\underset{\_}{X}\right)+{\epsilon }_{ijk}$in which, Y_ijk= value observed in the i-th diet, j-th sex and k-th repetition; μ= general average of the response variable; α_i= effect of the i-th diet; β_j= effect of the j-th sex; αβ_ij= effect of the interaction between the i-th diet and j-th sex; b₁= angular coefficient of the straight line of Y_ijk as a function of initial live weight (ILW) at fasting; X_ijk= initial live weight of the k-th animal under the i-th diet and j-th sex; $\underset{\_}{X}$= general average of initial live weight; ε_ijk= random effect associated with observation Y_ijk.

The data were investigated for outliers by means of the studied residual, tested for normality of error using the Shapiro-Wilk test. Subsequently, they were subjected to univariate analysis of variance using the general linear model’s procedure (PROC GLM - General Linear Models Procedures), their means adjusted using the ordinary least squares method (LSMEANS - Least Squares Means) and compared using the Tukey test at a 5% significance level. SAS software (SAS Institute Inc., Cary, NC, USA) was used for the statistical analysis.

RESULTS AND DISCUSSION

There was no interaction between diet and sex for dry matter and nutrient consumption and performance data, so the effects of diet and sex were analyzed separately. There was a difference in the lambs' intake of DM in relation to the type of diet provided (kg/day, %PV, g/kgPV^0.75) (P<0.05) (Table 3).

Table 3
Dry matter (DM) and nutrient intake of lambs kept in feedlot and fed roughage and/or concentrate diets

	Diet (D)			Sex (S)		Effect‡
	ROU	RCO	CON	Male	Female	Mean	D	S	DxS	CV1
kg
DM	1.40a	1.11b	0.80c	1.19A	1.01B	1.10	<0.0001	0.0003	0.70	9.7
TDN	0.81a	0.77b	0.64c	0.80A	0.68B	0.74	<0.0001	0.0002	0.28	9.5
CP	0.35a	0.20b	0.12c	0.25A	0.20B	0.23	<0.0001	0.0019	0.45	14.3
OM	1.19a	0.98b	0.74c	1.04A	0.90B	0.97	<0.0001	0.0010	0.67	10.3
NDF	0.52a	0.36b	0.19c	0.38A	0.33B	0.36	<0.0001	0.0263	0.80	15.4
ADF	0.33a	0.21b	0.08c	0.23A	0.18B	0.20	<0.0001	0.0020	0.05	16.4
%pv
DM	4.17a	3.63b	2.60c	3.62A	3.30B	3.46	<0.0001	0.0024	0.32	7.0
TDN	2.44a	2.44a	2.06b	2.45A	2.23B	2.34	<0.0001	0.0056	0.10	7.8
CP	1.07a	0.68b	0.39c	0.76A	0.70B	0.71	<0.0001	0.0203	0.28	13.8
OM	3.54a	3.23b	2.38c	3.17A	2.92B	3.05	<0.0001	0.0128	0.33	7.8
NDF	1.55a	1.18b	0.64c	1.17	1.18	1.12	<0.0001	0.1351	0.59	13.8
ADF	1.02a	0.70b	0.28c	0.71A	0.63B	0.65	<0.0001	0.0281	0.52	13.1
g/kg pv0.75
DM	88.81a	73.70b	5.80c	75.98A	68.42B	72.40	<0.0001	0.0014	0.07	7.1
TDN	58.01a	58.5a	48.42b	58.40A	51.59B	55.00	<0.0001	0.0025	0.24	9.5
CP	26.94a	17.14b	9.86c	18.57	17.46	18.00	<0.0001	0.4568	0.08	14.3
OM	86.03a	76.10b	53.85c	75.48A	75.48A	72.00	<0.0001	0.0064	0.72	8.4
NDF	38.00a	26.80b	15.18c	28.17	25.15	26.60	<0.0001	0.1699	0.43	20.8
ADF	25.99a	19.01b	7.98c	19.31	16.01	17.68	<0.0001	0.0503	0.82	23.6

• Means followed by distinct lower- and upper-case letters on the same line differ between diets and sex, respectively, by the Tukey test; ¹CV= coefficient of variation (%); ‡ D= diet effect; S= sex effect; TDN= total digestible nutrients; CP= crude protein; OM= organic matter; NDF = neutral detergent fiber; ADF= acid detergent fiber.

The lambs consumed a greater amount of DM when it consisted only of roughage (ROU). The alfalfa hay was fed ground with particles around one centimeter long, which may have led to higher consumption. Energy and protein are the main limiting factors, but some characteristics such as particle size can be important when it comes to understanding how animals use food. The lambs in the RCO treatment had an intermediate DM intake. Lambs in the CON treatment consumed less DM and this may be associated with the physical characteristics of the feed. Black oat grains have a fibrous layer that surrounds the germ and endosperm, as well as the pericarp, and therefore the grain is more resistant to microbial digestion (Sormunem-Cristian, 2013).

In our research, as we changed the concentrate content of the diet from 50% to 100% of the DM, the lambs ate less. This can be attributed to the main ingredient in the diet, around 50% (RCO) and 80% black oat grain (CON). In the study by Silva et al. (2023), in which confined lambs were given a diet containing 80% concentrate (made up of corn, soybean meal, wheat bran and calcitic limestone) and 20% ryegrass hay, they had a DM consumption of 3.98% of their live weight.

Chishti et al. (2022) they evaluated lambs fed chopped alfalfa hay with different levels of concentrate (0%; 20%; 40%) and observed an increase in consumption as the level of concentrate in the diet increased. In general, the ingredients used in the concentrate in the study are more palatable and more digestible when compared to the whole black oat grain used in the concentrate in this study.

Over the course of the experiment, there was a drastic variation in the animals' daily consumption of the CON diet, which may be associated with subclinical acidosis, but there were no clinical symptoms. The increased concentration of nutrients in the blood can stimulate chemical receptors that activate the satiety center, causing food intake to decrease or stop (Ferreira et al., 2013). Grinding the grains could facilitate digestion and, consequently, total consumption, affecting the rate of fermentation and the formation of end products, and then the composition of the rumen content (Andrés et al., 2018). Bernardes et al. (2015) researched the use of black oats in a high-grain diet for Texel lambs and found values for DM intake (0.730 kg/day; 2.74%PV; 62.09g/kgPV^0.75) and nutrients like our work.

There was a difference in nutrient intake (kg/day, % BW, g/kg BW^0.75) (P<0.05) for the diet treatment. And it may be associated with the intake of DM and the different levels of nutrients available in each diet, as well as the physical characteristics of the ingredients that may affect degradation by the microorganisms. Lambs from the ROU treatment had a higher nutrient intake, those from the ROC treatment had intermediate values and those from the CON treatment had a lower nutrient intake. Except for the consumption of TDN (%PV, g/kgPV^0.75) by the lambs on the ROU and RCO treatments, which were higher than the lambs on the CON diet (P<0.05). The NRC (Nutrient…, 2007) recommends a daily TDN intake of 560g/day for lambs weighing 30kg and an ADG of 200g. The lambs' TDN intake, regardless of treatment, is higher than recommended.

The NDF and ADF consumption values are higher than recommended. It is important to note that physical limitation can occur when the consumption of NDF is 1.2% of live weight (Van Soest, 1994). However, animals tend to exceed this limit when the diet has low energy levels, thus seeking to compensate for the dietary deficiency. CP intake varied from 350 to 120g/day, with the lowest intake for the animals given the CON diet (120g/day). Similar results were observed in the research by Sormunen-Cristian (2013) in which lambs fed whole black oat grain and hay at will have a crude protein intake of 129g/day. Lambs with moderate growth (200 g day^-1) and body weight over 30kg need to consume 131g/day of CP (NRC, 2007).

The final body weight was higher in the animals from the ROU treatment when compared to RCO (P<0.05) (Table 4). This result can be explained by the lower amount of energy available in the diet, so that a longer confinement period (approximately 94 days) was needed to store energy in the form of adipose tissue. In the research by Alhidary et al. (2016) lambs that received a total mixture control diet (TMR) with additions of 0.1kg, 0.2kg and 0.3kg of alfalfa hay obtained higher final body weights when compared to animals that only received TMR.

ADG was higher in lambs from the RCO treatment compared to the ROU treatment (P<0.05). This positive performance may be favored by the interaction between roughage and concentrate in the rumen, which may have caused an associative effect, promoting a series of changes in digestibility and nutrient utilization. The ADG of lambs increased with the use of the grain-rich diet (70% concentrate) compared to the diet with 70% roughage in the research by Trabi et al. (2019). Nascimento et al. (2020) found a higher ADG in lambs fed diets with higher proportions of concentrate and using hay as a source of roughage.

Table 4
Performance and feed efficiency of lambs kept in feedlot submitted to roughage and/or concentrate diets

	Diet (D)			Sex (S)		Effect‡
	ROU	RCO	CON	Male	Female	Mean	D	S	DxS	CV1
IW	23.82	23.02	24.51	24.48	23.09	23.7	0.402	0.129	0.56	10.1
SW	39.74a	35.31b	37.17a,b	39.50A	35.31B	37.5	0.002	0.0002	0.87	6.5
BCS	2.92	3.03	3.01	2.99	2.99	2.99	0.135	0.895	0.54	4.1
ADG	0.170b	0.215a	0.185a,b	0.222A	0.159B	0.18	0.011	<0.0001	0.41	15.9
DA	93.59a	56.45b	66.52b	72.66	71.70	72.55	<0.0001	0.863	0.47	18.9
FC	8.16a	5.29b	4.28c	5.49B	6.34A	5.82	<0.0001	0.011	0.96	13.1
FE	0.12c	0.19b	0.23a	0.20A	0.17B	0.18	<0.0001	0.003	0.45	14.5
BNE	12.46a	8.65b	5.67c	9.35A	8.50B	8.93	<0.0001	0.031	0.65	10.7

• Means followed by different lowercase and uppercase letters in the same line differ respectively, between diet and sex, using the Tukey test; ¹CV= coefficient of variation (%); ‡ D - effect of diet; S - effect of sex
• Slaughter weight (SW; kg) and initial weight (IW, kg), body condition score at slaughter (BCS; 1-5), average daily gain (ADG, kg), days spent in confinement (DA), feed conversion (FC (kg DM consumed/kg weight gain)), feed efficiency (FE (kg weight gain/kg DM consumed)) and bionutritional efficiency index (BNE).

Feed efficiency measured via FC, EE, and BNE indicated better feed utilization by the lambs on the CON treatment, followed by the lambs given the RCO diet (P>0.05). Lambs fed only roughage had the worst feed efficiency (P>0.05). In an intensive production system, producers indicate a feed conversion of 5.0 kg of feed/kg of weight gain, although this depends on the breeds involved and the type of diet provided (Van Der Merwe et al., 2020).

Bionutritional efficiency is more statistically correct for evaluating animal efficiency traits (Detmann et al., 2005). Determining the first canonical variable for ADG and DM consumption generated equations that determine the animals' bionutritional index: BNE= (-15.32 x ADG) + (10.75 x DM). The canonical coefficient associated with gain was negative and that associated with DM consumption was positive, so animals with a higher bionutritional index will be the least efficient (Mello, 2007).

As a result, diets with a high concentrate content tend to increase the efficiency with which the animals use nutrients. In addition, there is a consensus that diets rich in cereals reduce enteric methane production, however, it is important to note that this depends on the type of cereal (Popova et al., 2013). It is important to consider the cost of implementing diets, as well as having animals with genetics that provide excellent performance. Zootechnical indices related to feed consumption, growth rate and utilization of feed for growth are important for measuring efficiency and sustainability in a production system (Bello et al., 2016).

The lowest intake of DM expressed in different forms (kg/day; %PV; g/kg PV^0.75) was observed in females (P<0.05). Consequently, females consumed fewer nutrients. Except for the consumption of NDF expressed as %PV and CP, NDF, and ADF expressed as g/kg PV^0.75, where there was no difference between the sexes (P>0.05). This consumption behavior can be explained by the smaller size of the females, as well as the fact that they were slaughtered lighter because they are more precocious in depositing subcutaneous fat.

The males were slaughtered approximately 11% heavier and with a higher ADG than the females (P<0.05), which is possibly associated with greater muscle development. The females needed a lower body weight to obtain the stipulated body condition score, meaning that they deposited fat earlier and should therefore be slaughtered lighter. The slaughter weight of lambs is used as a parameter to assess the ideal time of slaughter (Sharifabadi et al., 2016; Van Der Merwe et al., 2020). However, the use of BCS as a tool for assessing the ideal condition for slaughter is more appropriate, especially when there are different sexes in the group of animals.

Regardless of the treatment (diet or sex), one of the possible causes that may have contributed to a reasonable ADG (average of 0.189 kg) in our study is genetics. The animals were sired by rams of meat breeds (the Suffolk breed), but the ewes had genotypes of breeds with lower gain potential, since the Lacaune breed has a dairy aptitude. Growth rate is an important economic characteristic because live weight at slaughter or carcass weight determines the producer's income from selling lambs (Posbergh & Huson, 2021). In an intensive production system, producers aim for an ADG of 300 g/day to obtain satisfactory results (Van Der Merwe et al., 2020).

The ingredient used in the concentrate may have contributed to this ADG, which is considered low for an intensive production system. The main ingredient used in feedlot is corn with a high starch content, but black oats contain a reduced amount of starch, meaning less available energy (Fruet et al., 2016) and the animals may possibly perform less well.

Feed efficiency measured via FC and EE was better in males (P<0.05). However, when it is evaluated using BNE, females are more efficient. This may be related to the smaller size of the males, as smaller animals will be more efficient as they are more precocious, diluting the maintenance requirements (Posbergh & Huson, 2021). Male lambs obtained a higher rate of gain because they consumed more and not because they are genetically more efficient at depositing fat, if the lambs (males and females) are in the same stage of body condition. In general, males have better zootechnical performance, but a lower percentage of coverage at slaughter (Facciolongo et al., 2018), meaning that when we aim to obtain homogeneous carcasses, the use of BCS is essential.

CONCLUSION

Regardless of how feed efficiency is assessed, the diet that provides the best results is the one containing 100% concentrate. Male lambs have a higher intake of dry matter, nutrients, and average daily gain than females, however, females have better bionutritional efficiency.

ACKNOWLEDGEMENTS

The authors would like to thank the Federal University of Santa Maria/ Rio Grande do Sul for providing the infrastructure to conduct this research and the financial support of CAPES. Thanks also to the Federal Institute of Education, Science, and Technology of Southeast Minas Gerais - Campus Rio Pomba for the financial support for the translation of the manuscript.

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Publication Dates

• Publication in this collection
  28 Apr 2025
• Date of issue
  May-Jun 2025

History

• Received
  17 June 2024
• Accepted
  04 Oct 2024