The present study included four experiments, two of them concerned with calves' behaviour and the other two concerned with ewes' and lambs' behaviour. Experiment 1: This experiment investigated the effect of sward complexity and sodium fertiliser application, on the behaviour and performance of calves. The study was carried out on sixteen Friesian calves, aged 5-6 months, with no previous grazing experience (eight males & eight females). The results obtained revealed that: 1. The application of sodium fertiliser to pasture resulting in an increase in the grazing time of calves. 2. The calves preferred grazing the sodium fertilised pasture and had a faster biting rate and faster walking rate on sodium fertilised pasture compared with the control. 3. The male calves had a faster biting rate and faster walking rate compared with the females on the all pasture treatments. 4. Grazing time and rumination time increased in up to three species but were reduced when a fourth (Red Fescue) was included. 5. The results showed that the calves are highly selective during grazing. They preferred grazing on Perennial ryegrass, followed by Timothy, Cocksfoot but not on Red Fescue. So, on those preferred grasses the calves had a faster biting rate and faster walking rate as well as a greater search distance 6. The increase in the grazing time of calves was accompanied by a decrease in the loafing time per day. 7. The time spent in rumination by calves during grazing was about three quarters of that spent in grazing. 8. The sward height significantly affected the grazing activities of calves. A decrease in sward height was accompanied by an increase in the grazing time, biting rate, and walking rate of calves. 9. The male calves had a greater search distance at grazing than the females especially on the sodium fertilised swards. 10. The sward species had a significant effect on the search distance of calves at grazing, and was greater when the calves grazed on Perennial ryegrass followed by Timothy then Cocksfoot. It was lower when grazed on Red Fescue. 11. There was a tendency for an increase in the search distance of calves grazing on the sodium fertilised pasture. 12. The calves during grazing drank 3.5-4.6 times/day and spent 1.5-2.0 min./day drinking. 13. There was no significant effect of the sward complexity on the drinking behaviour of calves. 14. The calves spent 39.7-65.0 min./day in body care activity and they had 9.6-13.0 body care bouts/day. 15. There was no significant effect of the sward complexity on the performance of calves, where their live weight and weight gain were not affected by the complexity of species. 16. The male calves had. a greater weight gain than the females during grazing. 17. The live weight and weight gain of calves were increased toward the fourth period of the experiment, due to the increase in grazing time. 18. The loafing time of calves was significantly decreased up to the fourth period of the experiment, due to the increase in grazing time and other grazing activities in the same direction toward the fourth period. 19. The application of sodium fertiliser to pasture resulting in a significant increase in the sodium content of the sward, ash content, DM content. Also, there was a tendency for potassium to be decrease but calcium and magnesium not significantly affected. 20. The sward species significantly affected its chemical composition. Perennial ryegrass, Timothy and Cocksfoot contained more sodium and magnesium than Red Fescue, but Perennial ryegrass had a greater crude protein content, followed by Red Fescue than Timothy and Cocksfoot which were nearly similar. Experiment 2: This experiment was concerned with studying sodium- conditioning in calves and the effect of addition of sodium chloride to the concentrate ration of early weaned calves on their maintenance behaviour, oral-purposeless activities and performance during their rearing period in a calf-pen house system.The study was carried out on sixteen early weaned heifer calves aged 7-9 days. The results obtained revealed that: 1. The addition of 0.5% sodium to the concentrate ration of calves resulted in an increase in the concentrate intake and water intake per day. 2. The calves which were supplied with sodium had a greater eating time on the concentrate and roughage than the control calves. 3. The addition of sodium to the concentrate resulting in a significant increase in the drinking frequencies of calves, as well as, in their drinking time per day. 4. The calves which were supplied with sodium began. rumination behaviour early and had a greater rumination time than the control group. 5. The calves which supplied with sodium had a lower loafing time than the control group. 6. The oral-purposeless activities e.g. ear-sucking and licking the wall of pen were decreased by the addition of sodium to the concentrate ration of the early weaned calves. Calf-kissing, licking-buckets and mouthing pen's door and buckets also tended to decrease with sodium. 7. The body care time and frequencies were decreased by the addition of sodium to the concentrate ration of calves. 8. The calves which were supplied with sodium had a heavier body weight at weaning than the control calves. 9. The results indicate that the concentrate intake and water intake were increased with age of calves. 10. The eating time and rumination time of calves were increased with the age. 11. The body care time and frequencies were increased with age of calves. 12. The loafing time of calves was decreased by the increase in their age. 13. licking The of the pen's wall and buckets was significantly affected by the age of calves, where the licking of buckets was increased with age but the licking of pen's wall was significantly decreased with age. Calf- kissing and mouthing the pen's door and buckets were not significantly affected by the age. 14. The calves which were supplied with sodium during their rearing period were conditioned on sodium. At the age of 6 months, the supplemented calves and the control calves were supplied with different levels of sodium mixed with siage. The group had been supplied with sodium during their rearing period preferred eating the silage with high level of sodium than the control group. 15. The conditioned calves had a greater silage, as well as DM intakes than the control group per level. The conditioned calves had the maximum silage and DM intakes at 0.8% of sodium but the control group reached their maximum intake at 0.3% of sodium. 16. The conditioned calves had a greater eating time and a greater rumination time, as well as greater drinking frequencies than the control group. 17. The conditioned calves had greater urination and defecation frequencies than the control group. 18. The pen housing system represented a kind of stress on the calves especially on their movement activity and play pehaviour, but the loose-housing was more comfortable for calves' activity and playing. Experiment 3: The aim of this experiment, was to investigate the effect of sward species-conditioning on the grazing behaviour of ewes and lambs. The study included 32 ewes, each with her single newly born lamb. The results obtained revealed that: 1. The ewes were spent 456-513 min./16h (daylight hours) in active grazing, during their conditioning period. 2. The young lambs were began the grazing trial at the 2nd- 3rd week of their age and spent 13.7-25.7 min./16h grazing at that age. in 3. The ewes during grazing in the conditioning-field spent 251-261 min/16h in rumination. 4. The decrease in sward height was accompanied by an increase in the grazing time of ewes and lambs. 5. The ewes became conditioned on Perennial ryegrass, Timothy, and Cocksfoot but to lesser extent on Red Fescue sward. However, the lambs did become conditioned on all four species. 6. The lambs at the 5th week of age spent 95-112 min./16h in active grazing. Experiment 4: The aim of this experiment was to investigate the effect of pre-weaning experience, presence of adult ewes, and sward complexity on grazing behaviour of fresh weaned lambs. The study included 40 lambs, aged three months, twenty of which were experienced by grazing with their mothers until weaning, but the other 20 lambs were not grazed before weaning. Five adult ewes were grazed with 10 lambs of the two groups during the experiment. The results obtained revealed that: 1. Experienced lambs had a greater grazing time compared with inexperienced lambs. 2. The lambs grazed with adult ewes had a greater grazing time than those grazed alone. 3. The grazing time of lambs complexity. as increased with sward 4. The lambs spent a longer time grazing on Timothy, followed by Perennial ryegrass, then Cocksfoot, and least on the Red Fescue sward. 5. The experienced lambs had a faster biting rate compared with the inexperienced lambs during their grazing. 6. The biting rate of lambs was not significantly affected by presence of adult ewes, but was significantly increased with the complexity of swards. 7. The lambs had a faster biting rate on Timothy, followed by Perennial ryegrass, then Cocksfoot, compared with Red Fescue. 8. The experienced lambs spent a longer time ruminating. Compared with the inexperienced lambs. 9. The lambs grazed with adult ewes had a longer rumination time than those grazed alone. 10. The rumination time of lambs was increased with the complexity of swards.