Study Of The Effect Of Different Ratios of Forage To Concentrate On Performance And Carcass Traits Of Zel Fattening Lambs

Fattening refers to the proper management and feeding of livestock to achieve maximum weight gain at a minimum cost over a specied period of time. This study aimed to determine the most effective ratio of forage to concentrate on feed intake, performance, and carcasses of male Zel fattening lambs. The present study was performed using 20 lambs of 16-week-old for 90 days in a completely randomized design with four treatments and ve replications at the Islamic Azad University of Qaemshahr. Experimental treatments included different ratios of forage to concentrate (80:20, 70:30, 60:40, and 50:50). Traits were measured during the fattening period. The collected data were analyzed by LSmeans procedure and regression in SAS software. Effect of different ratios of forage to concentrate was signicant on all performance traits (p < 0.01), slaughter weight (p < 0.05), weight gain during rearing (p < 0.05), daily weight gain (p < 0.05), feed intake (p < 0.01), feed conversion ratio (p < 0.01), the weight of digestive system contents (p < 0.05), hot and cold carcass weight (p < 0.05), carcass percentage (p < 0.05) and thickness Backfat (p < 0.05). The linear change in the mentioned traits is due to the increase of the concentrate to forage ratio (p < 0.01). As the percentage of concentrate in the ration increases, feed intake increases. The concentrate is palatable and contains more energy and nutrients than forage. Therefore, lambs that consumed more concentrate had higher body weight and slaughter weight. Based on the results for optimal performance in fattening lambs, a ration with the ratio of forage to concentrate equal (50:50) is recommended.


Introduction
One of the main strategies for producing animal protein is fattening. Fattening refers to the proper management and feeding of livestock to achieve maximum weight gain at a minimum cost over a speci ed period of time. On the other hand, the purpose of being weight gain is to provide the animal protein needed for human societies (Hosseini et al. 2019). Fattening using pastures is cheaper than intensive fattening, but will take longer. Also, the amount of overweight in this method is much less than the intensive method. Because some of the energy and nutrients that need to be stored in fattening animals are wasted on maintenance and walking. This method is not suitable for a country like Iran. Because the pastures of the country are not in a good condition. The number of grazing livestock is more than the capacity of pastures. Due to the decrease in rainfall and the increase in the number of livestock, the condition of the pastures worsens every year. Feeding lambs in pastures or with forage, although it may produce carcasses with a higher ratio of lean meat, will reduce the growth rate and produce lighter carcasses. In contrast, lambs fattening with concentrate-based rations increases the growth rate and production of heavier carcasses (Murphy et al. 1994). For lamb fattening in the intensive method, a feed consisting of forage and concentrate is used. Forage is brous in nature. Because of this, they cannot provide enough energy and protein to feed lambs. Therefore, this de ciency can be met by dense food in terms of energy and protein (concentrate). The right combination of forage and concentrate can create the best and most desirable performance in lamb fattening. The results indicate that the addition of concentrate to forage-based rations in ruminants by increasing the heat produced by visceral organs and reducing the energy of fecal dry matter and urinary nitrogen increases the production e ciency of these animals (Shi et al. 2018). When rations consisting of grains and forage are consumed, the e ciency of utilizing nutrients for the production of animal tissues usually increases (Nie et al. 2020). The appropriate ratio of forage to concentrate in the ration of fattening lambs is important. Traits related to lamb fattening in the intensive method depend on the ration's energy and protein levels (Borton et al. 2005;Nie et al. 2020).
Zel sheep is the only without tail fat breed in Iran. Instead of a tail fat, it has a narrow tail consisting of 7 tail nuts with a length of 10 to 15 cm. Lack of tail fat in Zel sheep has caused fat accumulation and storage in the tail fat is not done and stored between tissues. This has increased the quality and marketability of Zel lamb meat (Hosseini et al. 2019).
This study aimed to determine the best forage to concentrate ratio on feed intake, performance, and carcasses of male Zel fattening lambs.

Animals and treatments
The present study was performed using 20 male Zel lambs in the Islamic Azad University of Qaemshahr. The mean weight of lambs with a mean age of 16 weeks was 27.8±2. 1 A box was designed and considered for each lamb. Experimental feeds were randomly assigned to lambs. Water and feed were provided for each box. Thus, feed consumption was measured individually. The duration of the experiment was 90 days. Lambs were weighed every week after 10 hours of abstinence and at 6 a.m. The lambs were fed three times a day at 6, 14, and 20 o'clock to the point of appetite. Healthy water was constantly available to the lambs.

Traits measurement
At the end of the rearing period, three lambs from each treatment were randomly selected and slaughtered. All body parts and internal organs of each animal were separated and weighed. The carcasses were kept in the refrigerator for 24 hours at 4°C. Each carcass was then divided into two equal parts. The nal weight at the end of the experimental period was considered as the slaughter weight. The right half of the carcass was divided into pieces including neck, shoulder, brisket, ank, Rack-Loin, and legs. Then, they were weighed. Lean meat tissues, subcutaneous fat, intramuscular and bone fat were separated and weighed (Hosseini et al. 2019). To measure the cross-sectional area of the rack-Loin muscle or eye muscle, the area between the ribs 12 and 13 of the left carcass was cut, and its area was calculated using a Planimeter. The subcutaneous fat thickness of the left half carcass was measured on the transverse diameter of the eye muscle as the backfat thickness (

Statistical analysis
For the present study, a completely randomized experimental design with four treatments and ve replications was used. The collected data for the studied traits were recorded in the computer. LSmeans procedure and regression in SAS software (2000) were used for statistical analysis of data. The statistical model used was as follows: That; y ij , the amount of each observation; µ, the mean effect; T i , the treatment effect, and e ij is the residual effect.

Result
Performance traits As shown in

Carcass components traits
Studying the effect of different ratios of forage to concentrate on the traits of carcass components (table 5), it is observed that the difference between the mean weight of traits of carcass components was not signi cant (p>0.05). Based on the results of Table 4, it is observed that there is no linear and non-linear relationship between changes in carcass component traits and increasing the percentage of concentrate in the ration (p>0.05).

Performance traits
The change signi cantly in the treatment containing the equal ratio of forage to concentrate (P <0.01) be due to the presence of dense substances containing energy and protein in the feed. Therefore, livestock showed better performance by consuming more concentrate. These results The better response of livestock to a higher growth rate can be related to the increase in energy and protein concentration of the experimental rations. A number of researchers have reported that rations containing 70% concentrate stimulate the proper response of lambs and fattening calves to growth performance (Langlie 2020;Fimbres et al. 2002;Glimp et al. 1989;Mahgoub et al. 2000). They also reported that the effects of a high percentage of concentrate in the ration can be seen in the dry matter consumed by lambs (Hat eld et al. 1997;McLeod and Baldwin 2000), goats (Lu and Potchoiba 1990), and fattening calves (Lardy et al. 2004). The results of these studies are consistent with the results of the present study. The animal consumes the feed to provide the energy it needs. Once the energy needs are met, the appetite for food decreases. The highest and lowest performance was related to the lambs of the last and rst treatment, respectively (table 2). Improving the conversion ratio of rations by increasing the concentrate ratio can be due to the increase in energy and protein in the ration, which led to a better response of livestock.

Traits related to carcass quality
With increasing the percentage of concentrate in the feed of fattening lambs and consequently increasing the feed consumption, the mentioned traits were affected and changes were observed. Concentrate increases the palatability of the ration and on the other hand, the amount of energy and other nutrients in the concentrate is more than forage. Therefore, it seems natural that the traits presented in table 3 improve. Compared to concentrate, forager, in addition to being bulkier, also have the ability to absorb more water, which will increase the volume and, consequently, the weight of these substances in the gastrointestinal tract.
As the percentage of concentrate in the feed increased, the percentage of carcasses decreased linearly. It can be said that more contents of the digestive tract have negative effects on carcass performance. This means that more contents of the animal's digestive tract at the time of slaughter will reduce its carcass percentage.

Conclusion
As the percentage of concentrate in the ration, feed intake increases. The concentrate is palatable and contains more energy and nutrients than forage. Therefore, it is natural for lambs that consume more concentrate to have more body weight and slaughter weight. Due to the fact that the Zel breed is without tail fat, fat storage is done between the muscles and inside the abdominal area. Based on the results of the present study, for optimal performance in fattening lambs, a ration with an equal ratio of forage to concentrate (50:50) can be suggested.

Declarations
All the authors contributed to the study conception and design. Data collection was done by Seyed Mohsen Mousavi Kashani. Data analysis and manuscript preparation were performed by Shahabodin Gharahveysi and Kaveh Jafari Khorshidi. All the authors edited, read, and approved the nal manuscript.

Data availability
All data generated and analyzed during this study are included in this published article. Declarations The study was conducted at a commercial animal farm (Qaemshahr, Mazandaran province, north of Iran). All lambs' care and use procedures were approved by the Department of Animal Science, Islamic Azad University (Qaemshahr branch, Qaemshahr, Iran).

Consent to participate
Not applicable.

Consent for publication
All the authors give consent for publication.

Con ict of interest
The authors declare no competing interests