Effect of water restriction on aspects of digestion in Boer and Tswana goats offered Eragrostis teff and lucerne hay

Abstract

The first part of this study was undertaken to investigate the effect of water restriction on aspects of digestion in Tswana goats offered Eragrostis teff hay. Twelve Tswana goat wethers approximately 15 months old weighing on average 28.67 ± 4.48 kg, were randomly allocated to form three groups of four animals in each. The groups were all exposed to the following treatments: Water ad libitum (This served as control); 50% ad libitum water intake once in the morning, and 25% of ad libitum water intake in the morning and 25% ad libitum water in the afternoon. All the goats were adapted and fed Eragrostis teff. The final body weight of the ad libitum group was higher than that of treatment groups whilst no significant difference was observed between the water restriction treatments. Rectal temperature, heart and respiration rates were not affected by water restriction. Similarly haematocrit, total plasma protein, osmolarity and plasma urea levels were not affected by water restriction. Dry matter intake was reduced by water restriction from 848.69 to 740.16 g/d. Water to dry matter ratio dropped from 1.47 to 0.79. Faecal water was not affected by water restriction. However, urine output was reduced from 321.72 to 245 and 255.17 g/d for the half and quarter ad libitum water intake groups, respectively. Insensible water loss was at 549.7 g/d for the ad libitum water intake group compared to – 0.49 and 20.86 g/d of the half and quarter ad libitum water intake groups respectively. Water use efficiency was higher (p < 0.05) for the water restricted groups compared to the ad lib water group. Digestibility coefficients for DM, ADF, and NDF were all not affected by water restriction but apparent digestibility for nitrogen was reduced from 50.7% to 44%. Specific gravity of urine was higher (p< 0.05) for the water restricted groups while urea output and urea concentration were not significantly different among all the three groups. More of the nitrogen was lost through urine in all the groups leading to a negative nitrogen balance. The negative nitrogen retention was more pronounced in the water restricted groups. It was concluded that water restriction did not affect digestion and nutrient utilization of Tswana goats when offered Eragrostis teff. In part II of this study, the aim was to investigate the effect of water restriction on aspects of digestion in Tswana and Boer goat wethers offered either Eragrostis teff or Medicago sativa. Twentyfour goats (12 Boer and 12 Tswana goat wethers) of 12 – 15 months old weighing 18.3 – 32.8 kg were randomly allocated to form 4 groups of 6 goats. Within each group, there were 3 Boer and 3 Tswana goat wethers. These were used into a 4 X 4 Latin square design with the following treatments : (1) Water and teff ad libitum (2) 50% (Half ) of ad libitum water and teff ad libitum (3) Water and lucerne ad libitum (4) 50% (Half ) of ad libitum water and lucerne ad libitum. All the animals lost weight by the end of the water restriction period when fed either teff or lucerne. This weight was regained after a day of rehydration. Both Boer and Tswana goats lost 10% of their body weight when offered lucerne while water – restricted and then regained 13 – 14% of their dehydrated body weight. For both breeds, when teff or lucerne was offered, haematocrit, total plasma proteins, heart rate and rectal temperature were not affected by water restriction. Respiration rate increased in both breeds during water restriction. Plasma urea and osmolarity rose significantly from day 0 to day 4 but there was no significant difference between day 4 and the last day (day 7) when both breeds were fed either teff or lucerne .Regardless of the breed and treatment, water restricted goats had lower water use efficiency and higher urine specific gravity values compared to ad libitum water groups. On teff, water restriction did not have any significant (p>0.05) influence on dry matter intake but faecal dry matter was reduced (p< 0.05) from 360.15 to 315.16 g/d. The water to dry matter ratio was reduced (p< 0.05) from 1.71 to 0.83. The digestibility coefficients for DM, N, ADF, and NDF were unaffected by water restriction. However, ADF and NDF digestibility coefficients were higher than those of DM and N. On lucerne, dry matter intake was significantly (p < 0.05) reduced from 1022.75 to 756.28 g/d while faecal dry matter output decreased from 384.33 to 292.15 g/d. The water to dry matter ratio dropped significantly (p < 0.05) from 2.32 to 1.29. The digestibility coefficients did not differ between the ad libitum and half ad libitum water groups. However the digestibility coefficients for ADF and NDF were lower than those of DM and N. Water restriction did not improve nitrogen retention when either teff or lucerne was offered in both Tswana and Boer goats. It was concluded that goats are efficient in utilizing water and digesting high fibre feedstuffs when water is limited. However, both breeds did not display evidence for a mechanism of improving nitrogen retention when fed low and high nitrogen feedstuffs (teff and lucerne, respectively) while water intake is restricted.