Milos Lukic’s research while affiliated with Institute for Animal Husbandry and other places

The aim of the present study was to evaluate the effects of adding protease enzymes (Ronozyme ProAct, 0, 200 mg/kg and 300 mg/kg diet) while reducing the crude protein content (control group - standard diet, group E-I - 4 % less crude protein compared to the control group and group E-II, which received 6 % low-protein feed compared to the control group) in fast and medium-growing meat chickens on the weight and percentage of certain classes of meat. In the experiment, fast-growing Cobb 500 and medium-growing Master Gris chickens were used. The genotype had a significant effect on the weight and percentage of the different chicken meat classes (P<0.05). The fast-growing Cobb 500 genotype had a higher weight of all meat classes and a higher percentage of meat class I and a lower percentage of meat class II and meat class III compared to the broilers of the Master Gris genotype (P<0.05). Significance was found under the influence of the protease enzyme in the hybrid Cobb 500 for meat class III (between C group and E-I group on the one hand and E-II group on the other hand, P<0.05) and in the hybrid Master Gris for meat class III (between C group and E-I group, P<0.05), while there was no effect on the mass of all three classes of meat (P>0.05). Enzyme protease can be used as an additive in a broiler diet for production at a concentration of 200 mg/kg Ronozyme ProAct and with 4% less crude protein compared to the standard diet. Keywords: broilers, hybrids, enzyme protease, classes of meat.

This study aimed to explore how hybrid varieties impact broiler chickens’ production and slaughter performance. We applied standard rearing techniques over a 42-day period. The trial involved a total of 420 broiler chickens of the following hybrids: Cobb 500 and Ross 308. Weekly performance tests were conducted, assessing average daily gain, feed consumption, feed conversion rate, mortality, and European Poultry Efficiency Factor. After controlling for final body weights on the 42nd day, a random sample of 12 broilers per genotype, with an equal gender distribution, was selected for slaughter parameter analysis. Following slaughter traits were determined: pre-slaughter weight of chickens, slaughter yield, share of abdominal fat, chicken thigh circumference, and chest angle. The results revealed no significant difference in food consumption between the examined hybrids. Chickens of the Cobb 500 genotype exhibited significantly higher (p<0.01) gain and a more favorable feed conversion rate. Due to its better vitality, feed conversion rate, and gain, Cobb 500 chickens demonstrated significantly higher (p<0.01) European Poultry Efficiency Factor values. In contrast, Ross 308 chickens displayed statistically significantly lower (p<0.05) slaughter yield and chest angle values. At the same time, the proportion of abdominal fat and chicken thigh circumference showed no significant difference between the tested hybrids.

The objective of the study is to determine the share of eggs from non-cage production systems compared to eggs from cage systems, in the year when the extended transitional period expires (December 2023) for Serbian producers to comply with the welfare legislation, mandating the transition from the conventional cage breeding system to permitted systems (enriched cage system and non-cage systems (floor, aviary, free breeding - free ranges, organic production). Also, the objective of the study is to determine the structure of consumers within the group valueing the breeding system, which declares that it prefers free range eggs and organic eggs. The examination of the Belgrade market supply of eggs, including supermarkets (11), green markets (5) and specialized stores (5), and consumer attitudes was conducted through a survey (247 respondents in the Belgrade region). According to the results of the survey, it can be concluded that the supply of eggs from non-cage systems is minor, compared to eggs from the cage system, which have a share of 100%, it is 81.82% for eggs from the floor system, 54.54% for eggs from free range and 9.10% for organic eggs. The supply of organic eggs on the market is insufficient and mainly associated with specialized stores. For about 30% of consumers, the egg production system is very important, whereby the majority of consumers (53.45%) would prefer the eggs from free ranges, and among them the largest share are women (76.03%), consumers with higher education (67.10%), employed (78.38%), aged 36-55 and with higher monthly incomes. Based on the research results, it can be concluded that the process of harmonizing egg production with welfare regulations has an impact on the egg market, i.e. resulting in changes in the sense of greater share of eggs from non-cage systems compared to similar research in the earlier period. At the same time, although there is a growing awareness among consumers about the importance of the production/rearing system, it is still insufficient compared to certain European countries. The development of non-cage systems, as more favourable from the point of view of welfare and consumer expectations, should be given greater attention in the coming period, by acting through regulatory measures, education of producers and consumers, research and support in terms of incentives, subsidies and loans to producers who switch to alternative systems of raising laying hens.

The aim of the study was to evaluate the effect of three protein levels (with or without protease enzymes) on the weight and percentage yield of each meat class in two genotypes of broiler chickens (fast-growing hybrid Cobb 500 and medium-growing hybrid Master Gris). Each genotype was divided into a control group (C group) fed with a commercial feed mixture and an experimental group fed with a low protein diet of 4% (E-I group) or 6% (E-II group) in relation to the control group, with the addition of 200 mg/kg Ronozyme ProAct (E-I group) or 300mg/kg Ronozyme ProAct (E-II group). Weight and percentage yield of the meat classes were influenced by the genotype. The fast-growing hybrid Cobb 500 had higher masses of all meat classes and a higher percentage of class I meat, while the percentage of class II and III meat was lower than in the medium-growing hybrid Master Gris (P<0.05). Feeding had no effect on the weight and percentage yield of the individual meat classes in either hybrid (P>0.05).

In order to preserve indigenous and locally adapted breeds through development programs for sustainable egg and meat production, it is necessary to have more data on the potential of these breeds in different production conditions. Accordingly, the objective of the study was to determine and compare the reproductive potential, production performance and egg quality of two indigenous poultry breeds: the Banat Naked Neck (BNN) and the Svrljig Hen (SH), in improved growing conditions (nutrition, photoperiod and housing) in relation to the traditional rearing of these breeds. Four flocks for each breed were housed in floor pens in a closed facility during the winter months, and then in the vegetation season (April-September) they were kept in mobile cages in the pasture. The duration of the photoperiod in the facility was 15 hours, and in the pasture, they were exposed to the natural duration of daylight. The layers were fed ad libitum with balanced complete mixtures for layer-line hybrids and during the vegetation season supplemented with food found in the pasture around the mobile cage. The reproductive potential of BNN and SH hens was determined on the basis of the age of the hens at the beginning of laying, the age at the peak of laying and the number of eggs per housed hen. The egg hatching properties were examined based on the percentage of chicks hatching in relation to the number of laid and fertilized eggs. Data on the quality of table eggs were obtained by testing over eight-week periods during the entire laying period. Under the applied rearing, nutrition and photoperiod conditions, BNN hens achieved production in accordance with their genetic potential defined by the breed standard, while SH layers with 126.43 eggs/housed hen achieved production higher than the breed standard. The egg production of these two breeds of hens differed in the intensity and persistence of laying, which, in addition to a higher peak of laying, resulted in a higher production of egg/housed hen BNN (146.71) compared to SH. On the other hand, parameters of table egg quality, i.e., shell quality and egg albumen/yolk ratio, were significantly better in SH. Also, SH had a higher reproductive potential compared to BNN hens based on the percentage of fertilized and hatched eggs.

This study aimed to assess the effects of different dietary levels of the protease enzyme and sex on skin, bone and muscle yields and percentages of breast, drumsticks and thighs as the most valuable carcass parts of broilers. A total of 300 one-day-old, mixed-sex broiler chickens (Cobb 500) were randomly divided into 3 dietary treatments with different levels of protease supplementation (group C: a standard diet without Ronozyme ProAct; group E-I: a diet with 200 mg/kg Ronozyme ProAct and a 4% crude protein reduction compared to the standard diet; and group E-II: a diet with 300mg/kg Ronozyme ProAct and a 6% crude protein reduction compared to the standard diet). All diets were maize- and soybean meal-based. Feed and water were provided ad libitum throughout the 49-day feeding trial. The results obtained indicate that the dietary treatments had no significant effect on skin, bone and muscle yields and percentages of the drumsticks, thighs and breast (P > 0.05), except for the breast muscle weight in the female chickens (especially between the E-I and E-II groups), and the drumstick bone percentage in the males between the C and E-2 groups (P < 0.05). In all three groups, the male chickens exhibited higher weights of skin, muscle and bone in breast, drumsticks and thighs than the female chickens, and the differences were not significant only in the skin weight of drumsticks and thighs (P > 0.05). The females had a higher yield of muscle tissue in breast and drumsticks, a higher percentage of skin in drumsticks and thighs, and a lower percentage of bone in drumsticks and thighs than the males (P < 0.05). Major differences resulted from the effect of broiler sex, whereas the dietary treatments containing 3 levels of protease supplementation had a very small effect on the yields and percentages of skin, bone and muscle in breast, drumsticks and thighs.

The first few weeks after broilers hatch are the period of most intense bone growth and development, and the time when they are most susceptible to the influence of various external and internal factors. Research in the recent decades has focused on the involvement of melatonin in bone development during early life in chickens. Melatonin release from the pineal gland has a circadian rhythm, with the highest levels circulating during the night and decreasing during the light phase of the day. Various types of lighting are used in intensive broiler production. In this study, the effects of melatonin on the tibial structure and growth of broilers were investigated. During the first two weeks of life, two groups of chickens were kept under continuous light and fed the same diet, with the experimental group receiving melatonin in the amount of 0.03 g/kg of feed. The results obtained showed that the addition of melatonin in the diet had positive effects on the development and growth of the tibia, which was expressed in a significantly greater thickness of the diaphysis and cortical bone of the diaphysis, higher breaking force and higher values of alkaline phosphatase activity. The cortical bone mineral density of the tibia did not differ significantly between the groups of chicken.

The objective of the present trial was to evaluate the effects of nettle leaves (Urtica dioica) supplementation, broiler gender and muscle portion on meat fatty acid and mineral profiles. Prior to the trial, a total of 600 one-day-old Cobb 500 broiler chickens of both genders, equally, were randomly divided into three groups: a basal diet (control group) and a basal diet supplemented in the last two weeks of fattening with fresh nettle leaves (30 g/kg diet) or with oven dry nettle leaves (5 g/kg diet). After reaching 42 days of age, twenty birds per diet group were randomly selected (four birds per box, both genders equally) and slaughtered, and breasts and drumsticks were collected for analysis. The dry nettle supplementation increased the MUFA and lowered the PUFA, n-6 and n-6/n-3 ratio, mainly in female broilers (p < 0.05). Drumsticks had higher MUFA and PUFA and lower SFA and n-6/n-3 ratio compared to breast meat (p < 0.05). The addition of nettle to broiler diet increased Fe, Zn and Se and decreased Ca levels, mainly in drumsticks (p < 0.05). Furthermore, drumstick meat had more elements with proven health benefits, such as Fe, Zn, Ca and Mn, than breast meat. This study suggests that feeding Cobb 500 broilers with the addition of nettle leaves can significantly change meat fatty acid and mineral composition, but this effect differed between gender and portion.

The effects of feeding low dietary crude protein with supplemental protease and sex on the weight and percent yields of individual meat classes in broiler chickens of hybrid Cobb 500 were investigated. A total of 300 day-old broiler chicks were fed with one of the following three experimental diets: control group (C), the experimental group I (E-I) contained 4% less crude protein than the control (C) and were supplemented with protease (Ronozyme Pro Act) at a concentration of 200mg/kg feed and the experimental group II (E-II) contained 6% less crude protein and were supplemented with protease (Ronozyme Pro Act) at a concentration of 300mg/kg feed. Supplementation of protease to diets had no significant effects on weights of individual meat classes (P>0.05), as well as the percentage of meat classes, and the only differences were manifested between E-I and E-II (P<0.05, female broilers from the E-I group were had a higher percentage of class I meat and a lower percentage of class III meat compared to females from the E-II group). The effect of sex was manifested in the weights of all meat classes and the percentage of class I meat and class III meat (P<0.05).