The activity of some digestive enzymes in domestic rabbits before and after weaning

Effect of Type and Dietary Fat Content on Rabbit Growing Performance and Nutrient Retention from 34 to 63 Days Old

The study was carried out on individually and collectively housed growing rabbits from 34 to 63 days of age. Two experiments were conducted using three fat sources: Soybean oil (SBO), Soya Lecithin Oil (SLO), and Lard (L; Exp. 1), and SBO, Fish Oil (FO), and Palm kernel Oil (PKO; Exp. 2), added at two inclusion levels (1.5 and 4.0%). In both trials, 180 rabbits were housed in individual cages and additional 600 rabbits in collective cages from day 34 to 63. Animals fed with 4% dietary fat showed lower Daily Feed Intake (DFI) and Feed Conversion Ratio (FCR) than those fed with 1.5%, except in the individually housed animals in Exp. 1. In the collective housed group in Exp. 1, DFI was a 4.8% higher in animals fed with diets containing lard than those fed with SBO (p = 0.036). Lard inclusion also tended to reduce mortality (p = 0.067) by 60% and 25% compared with SBO and SLO diets, respectively. Mortality was the highest with the higher level of soya lecithin (14% vs. 1%, p < 0.01). A similar mortality rate was observed in the lowest level of SBO. In the grouped-housed animals in Exp. 2, a decrease of DFI (-12.4%), Bodyweight (BW) at 63 d (-4.8%), and Daily Weight Gain (DWG) (-7.8%) were observed with the inclusion of fish oil (p < 0.01) compared to other fat sources. Fish oil also tended to increase (p = 0.078) mortality (13.2%) compared with palm kernel oil (6.45%); similar results were found when animals were individually housed. The overall efficiency of N retention (NRE) increased with the highest level of fat in Exp. 1 (34.9 vs. 37.8%; p < 0.0001). It can be concluded that lard and palm kernel oil are alternative sources of fat due to the reduction of mortality. The inclusion of fish oil impaired animal productivity and increased mortality. An increment of the dietary fat level improved FCR and overall protein retention efficiency.

Effect of weaning diet and weaning age on growth, body composition and caecal fermentation of young rabbits

Two weaning diets (C and S) and three weaning ages (21, 25, and 28 days) were compared in a two factorial arrangement to evaluate their effect on growth performance, body composition and caecal fermentation activity of young rabbits. One hundred litters born the same day from multiparous does were used. Sixty litters were early weaned at 21, 25 and 28 days of age (20 litters per weaning age), put in collective cages (nine kits per cage) (W21, W25, and W28 litters) and offered the control diet C (crude protein (CP) : 175 g/kg dry matter (DM); ether extract : 20 g/kg DM; starch : 157 g/kg DM; acid-detergent lignin (ADL) : 60 g/kg DM; digestible energy (DE) : 11·08 MJ/kg DM) or the starter diet S (CP : 173 g/kg DM; ether extract : 41 g/kg DM; starch : 112 g/kg DM; ADL : 51 g/kg DM; DE : 11·31 MJ/kg DM). At 32 days of age, 180 early weaned rabbits (three rabbits from each of the 60 litters above) were selected : 60 animals were slaughtered; 120 animals were placed into individual cages and offered a fattening diet (CP : 166 g/kg DM; ether extract : 23 g/kg DM; starch : 177 g/kg DM; ADL : 49 g/kg DM; DE : 11·26 MJ/kg DM) from 32 to 56 days of age. At 56 days of age, another 60 representative rabbits were slaughtered. The administration of diet S to the early weaned rabbits increased litter weight at 32 days (6160 v. 6027 g;P<005) and gain to food ratio from weaning to 32 days (752 v 666 g/kg;P<0001) compared with diet C. Moreover, empty bodies (EB) of S rabbits were fatter (fat : 45 v. 41 g/kg; P = 001) and had greater energy content (5·92 v 5·71 MJ/kg;P<001). At 56 days of age, no residual effect of the diet was recorded. Weaning age affected growth performance, body composition and caecal fermentation at 32 days of age : EB weight (P<005) and EB protein concentration increased (from 164 to 168 g/kg,P<0·01) while caecal volatile fatty acid concentration decreased (from 71·7 to 53·8 mmol/l;P<0·01) when weaning age was increased from 21 to 28 days. At 56 days of age, no effect (P > 0·05) of weaning age was recorded on growth performance or caecal fermentation traits, but EB protein remained lower in the earliest weaned rabbits (P<0·05). In conclusion, feeding a high-fat low-starch diet to early weaned rabbits stimulated growth and body fat and energy retention of kits at 32 days of age with no effect on caecal fermentation. The early weaning successfully performed at 21 days of age strongly stimulated caecal fermentation but reduced body protein reserves.

Feeding strategy for young rabbits around weaning: a review of digestive capacity and nutritional needs

The digestive maturation of the young rabbit is reviewed. It indicates that their nutritional needs and those of lactating females are antagonistic in many aspects. Energy requirements of lactating females are very high, whilst a low starch, high fibre diet around weaning improves the health of the young after weaning. To solve this problem, several feeding and management strategies are presented and discussed. If weaning occurs between 28 and 35 days of age, feeding the young with a specific diet, different from the female’s, seems an effective solution. Otherwise, it is necessary to find a compromise between the needs of the litter and of the doe. Early weaning (< 26 days) could be also a promising way to provide adequate feeding for the young as soon as they begin to eat solid food.

Adaptability of the digestive function according to age at weaning in the rabbit: I. Effect on feed intake and digestive functionality

The functional adaptability of the digestive system to the level of feed intake was investigated in the young rabbits by comparing two groups of 12 litters each, weaned at 21 (W21) or 35 (W35) days of age. From 14 days onwards, rabbits were fed a pelleted feed (NDF: 332 g/kg, CP: 177 g/kg, starch: 98 g/kg, as-fed basis). Until 49 days of age, the profile of digestive enzymes was weekly determined in the small intestinal content and mucosa, as well as caecal fermentation traits and fibrolytic activities. In the W21 group, the solid feed intake was increased by 57% between 21 and 35 days (P < 0.01), while the daily body growth was lower from 21 till 42 days (-17%, P < 0.05) when compared with the W35 group. Activities of enzymes of pancreatic origin were only scarcely influenced by the weaning age. In the W21 group, amylase activity tended to be lower at 28 days of age (-36%, P = 0.064), and trypsin activity was decreased by 31% at 49 days of age (P < 0.01). Lipase activity was similar in both weaning groups. Duodenal and jejunal activities of maltase and aminopeptidase N (APN) were higher on day 28 in the W21 group as compared with the W35 group (×1.4 to ×2.4, respectively, P < 0.05). On day 35, duodenal APN activity was twice as higher in the W21 group than in the W35 group (P < 0.01). In caecum, major differences between both weaning groups were observed at 28 days of age with a decrease in ammonia concentration (-43%, P < 0.01) in W21 compared with W35 rabbits. Conversely, the acetate proportion was 5% higher in the W21 group (P < 0.01) on day 28. In conclusion, the digestive tract of early-weaned rabbits showed some adaptative properties in response to nutritional environment changes, but they were insufficient to maintain their growth rate.

Adaptability of the digestive function according to age at weaning in the rabbit: II. Effect on nutrient digestion in the small intestine and in the whole digestive tract

The ability of young rabbits to digest a solid diet was evaluated according to the weaning age: 21 (W21, 12 litters) or 35 (W35, 12 litters) days of age. From 14 days onwards, the rabbits were fed the same pelleted feed. Three methods were compared to estimate the faecal digestibility in the young rabbits, between 24 to 28 and 38 to 42 days. Digestive balance at ileal and faecal levels was determined for the main nutrients provided by milk and solid feed. The W21 rabbits increased their solid feed intake only 2 days after their weaning, when compared with suckling rabbits. Thus, their crude protein (CP) intake remained lower until 26 days compared with the W35 rabbits (from 41%, P < 0.01), as well as their crude fat intake until 28 days (from 72%, P < 0.001). On the contrary, the W35 rabbits increased their solid feed intake without a delay after weaning, quickly reaching the intake level of the W21 rabbits. The amounts of organic matter (OM) and CP reaching the caecum were increased on day 28 by 56% and 42% in the W21 rabbits compared with the W35 rabbits, respectively (P < 0.05), and were similar between groups on day 42. Starch ileal digestibility coefficients were 94·2% and 95·4% in 28- and 42-day-old rabbits, respectively, irrespective of the weaning age. The amount of starch flowing through the ileo-caecal junction was low and only tended to be higher on day 28 in the W21 group (0.20 v. 0.15 g/day in the W35 group, P = 0.10). The digestive balance pointed out that the digestible energy intake was similar between weaned and suckling rabbits from 23 to 27 days, a phenomenon partly explained by a high ability of the W21 rabbits to digest starch (98%) and NDF (36%). Indeed, the amounts of starch and NDF digested by the W21 group were 2.0- and 2.4-fold higher than those of the W35 rabbits at this period (P < 0.001). However, they ate 20% less digestible proteins than still-suckling rabbits (P < 0.001). From 38 till 42 days, only a lower ability of the W21 rabbits to digest lipids was detected (P < 0.05). In conclusion, early-weaned rabbits were able to adapt quickly to digest large amounts of starch and fibres.

Maturation of the intestinal digestion and of microbial activity in the young rabbit: Impact of the dietary fibre:starch ratio

The developmental changes of intestinal digestive potential and caecal microbial activity were described in suckling and weaned rabbits according to two feeding programmes. Two groups of thirteen litters were fed from 18 to 42 days old a "High" or a "Medium" NDF:starch ratio diet (resp. 2.7 vs 2.0, groups HL and ML) with similar protein and lipid levels, and from 42 to 70 days old the two groups were fed a "Low" NDF:starch ratio diet (1.7). From 25 to 32 days (weaning), the milk and solid feed intake were 22% and 41% higher in ML group (P<0.05), and the mortality by diarrhoea was 4 units lower (P<0.01). The whole tract digestive efficiency increased by 10% before weaning, and remained steady (organic matter) or decreased (lipids, protein) after weaning. Energy digestibility was 0.623 and 0.686 for High and Medium diets respectively. From 25 to 42 days, total enzymatic activity in intestinal content increased for chymotrypsin (5-fold, P<0.001), lipase (10-fold, P<0.001), amylase (17-fold, P<0.01) and maltase (11-fold, P<0.001), while trypsin doubled after weaning. The feeding programme only affected the amylase and maltase activities, that were higher in HL group (P<0.05). The volatile fatty acids concentration in the caecum was not significantly different among the groups, but it increased by 44% 10 days after weaning. The bacterial fibrolytic enzymes, increased by 30% after weaning and were similar among the two groups. The study revealed that the intestinal digestive maturation and the caecal microbial activity of the rabbit evolved markedly between 3 and 5 weeks of age, and was weakly affected when the NDF:starch ratio decreased from 2.7 to 2.0.

Digestive tract development in rabbit according to the dietary energetic source: correlation between whole tract digestion, pancreatic and intestinal enzymatic activities

The developmental changes of both pancreatic and intestinal enzymes and the influence of dietary composition on enzyme activities were followed in suckling and weaning rabbits. In addition, whole tract digestibility of nutrients was recorded in response to two dietary energetic sources. Rabbits were fed ad libitum either a low fat and high starch diet (group LF), or a high fat and high fibre diet (group HF) between d 32 and d 42, with both groups receiving a growing finishing diet thereafter. Before weaning (d 32) nutrient digestion was high (>75% for organic matter, protein or fat), and then decreased sharply, except for fat. Between d 32 and d 42, digestion in the HF group was 7.5 and 4.6% lower, respectively, for organic matter and protein, while fibre and fat digestion was higher (+14.0 and +5.0%, respectively). Between d 25 and d 42 of age, pancreatic-specific activities of trypsin and chymotrypsin did not change while those of amylase and lipase increased by 1.5- and 76- fold (P<0.05), respectively. However, total activities and relative activities expressed on a LW basis were increased after weaning as a main consequence of a specific increased organ weight and pancreatic protein content. Relative activities of trypsin and chymotrypsin increased by 63 and 56% (P<0.01) after weaning, respectively. Total activities of pancreatic enzymes measured in the total small intestinal contents increased during the same period, but the range of variations was lower than those measured in the pancreatic gland. Total activities of lipase, trypsin and chymotrypsin measured in the small intestine contents were significantly correlated with pancreas enzyme potentialities. Total small intestine activity of lipase was 58% higher (P<0.001) in HF than in LF group while the other pancreatic and intestinal enzyme activities measured were not influenced by the energetic sources of the diet. Decreased digestibility of organic matter and protein observed with the HF diet could not be related to changes in pancreatic or intestinal enzymatic profiles and may be more dependent on quality of dietary ingredients.