| Gama-aminobutyric acid (GABA) is one of the most important neurotransmitter in central nervous system, and has many regulatory functions on the animals. Many researches have been conducted with mono-gastric animals on the effects of GABA. However, there are few reports on ruminant animals. Due to the ruminal degradability of GABA, rumen-protected technology of GABA was developed to make GABA available in ruminants. A kind of rumen-protected (RP-GABA) which is stable in rumen but released efficiently in post-rumen digestive tracts was developed; the selected RP-GABA was then used to determine the effects of RP-GABA on feed intake and milk performance in transition and early lactating cows; finally, mechanisms of GABA on dairy cows were investigated by changes in serum variables and expression of feed intake related genes.1. Preparation of RP-GABA (Trail1)As GABA could be easily degraded in rumen, it should be protected before it can be applied in ruminant animals. The trail was conducted to prepare RP-GABA of high rumen-protected rate and intestinal digestive rate. Nine samples were designed and prepared, according to orthogonal design L9(34). GABA content, coating materials and air pressure were defined as the variations of preparation protocol. Dissolution rates were measured and four products with lower dissolution rates were selected to determine the ruminal and post-ruminal dissolution rates. The study was then conducted to estimate the dissolution rates of RP-GABA with the methods of in vitro and in sacco. All products had lower degraded rates than that of unprotected GABA (almost degraded within2h). Post-ruminal dissolution rates of the four products were over90%, indicating that they can be almost dissolved. All products had dissolution rates above90%in the digestive tract and the total digestive rates of were estimated to be from49.2%-75.8%. In summary, within the three factors (coating material, air pressure and GABA content), coating material played the key role in stability of RP-GABA. RP-GABA (50%GABA content, solid palm fatty acid pelled, air pressure11kp) was of low dissolution rate and high post-ruminal dissolution rate, and was selected to be used in all the following in vivo trails. 2. Effects of GABA on feed intake and lactating performance in Holstein dairy cows (Trail2and3)Transition and early lactating are critical physiological periods for Holstein dairy cows. Feed intake of both transition and early lactating cows may not meet the requirements of the increasing milk yield. Thus, feed intake of these cows is a key issue for dairy nutrition. Thus, prepared RP-GABA was applied to investigate its effects on transition and early lactating cows.2.1Effects of dietary GABA on feed intake and lactating performance in transition dairy cows (Trail2)Transition cows:Forty multiparous cows were blocked based on previous milk production, parity, estimated calving date and body weight and were randomly assigned to one of four treatments and received either no GABA (control) or were supplemented with non-protected GABA (1.2g/day) or RP-GABA (1.2and2.4g/day (GABA=0.6and1.2, respectively)), respectively. The experiment lasted from2weeks before calving to4weeks after calving. Milk yield and milk composition were recorded weekly. The results showed that, during3rd and4th week, cows fed1.2g/d GABA had higher feed intake, and higher milk protein yield (4th week), compared with that of the control.2.2Effects of dietary GABA on feed intake and lactation performance in early lactating dairy cows (Trail3)Forty-eight multiparous cows were blocked based on days in milk (DIM), milk production and parity and were randomly assigned to one of four treatments with RP-GABA added at levels of0,0.8,1.6or2.4g/d (GABA=0,0.4,0.8, and1.2, respectively), respectively. The experimental period was8weeks. Milk yield and milk composition (fat, true protein, lactose) were recorded weekly. Results indicated that cows fed GABA consumed more grass hay (P<0.05). Cows consumed0.4g/d GABA were of higher milk yield (P<0.05), compared those of the control, but yielding off when cows consumed1.2g/d RP-GABA. Milk protein yield increased in the cows fed0.4or0.8g/d RP-GABA, respectively. No difference was observed in either fat or protein contents of milk. Cows fed0.4and0.8g/d GABA had higher lactose contents, compared with those of the control (P<0.05). In summary, dry matter intake and milk performance could enhanced dose-dependently in cows fed GABA.In summary, GABA enhanced milk performance by increasing feed intake in Holstein dairy cows.3The mechanism of GABA on dry matter intake in dairy cows (Trail4and5)In mono-gastric animals, GABA mainly regulated feed intake through neuropeptide Y (NPY) and cholecystokinin (CCK) pathways. However, the mechanism is not clear in dairy cows. Thus, the current study was conducted to investigate the mechanism of GABA in feed intake regulation in dairy cows, by determining serum variables and genes expression related with feed intake (with Hu sheep as model).3.1Effects of GABA on serum variables in dairy cows (Trail4)In trail2, sera of transition cows were collected weekly. Serum contents of NPY, CCK, leptin and biochemical and antioxidative metabolites were analyzed weekly and the calving day. In trail3, sera of early lactating cows were collected in the1st,4th, and7th week, and serum contents of GABA, neuropeptide Y, and biochemical and antioxidant variables were analyzed. The results indicated that feeding1.2g/d GABA enhanced serum SOD (super oxide dismutase), GSH-Px (gluthathione peroxidase) and T-AOC (total antioxidation capacity) contents, decreased serum NEFA contents, and decreased serum CCK contents during3-4week after calving, compared with that of the control (P<0.05). No difference was observed in leptin among all treatments. For early lactating cows, animals fed0.8g/d GABA had higher GSH-Px and lower malondialdehyde (MDA) contents in sera, compared with those of the control (P<0.05). All cows fed GABA were of low NEFA contents (P<0.05). GABA did not change serum NPY contents in both studies. In summary, GABA enhanced anti-oxidative capacity and health condition. GABA enhanced feed intake through pathway related with CCK.3.2Effect of GABA on gene expression related with feed intake (Trail5)Twenty-four Hu lambs weaned at age of50d were divided into three groups of eight lambs each, with four units of two lambs in each group, based on body weight, and were randomly assigned to three dietary treatments with addition of RP-GABA at levels of0,140or280mg/d (GABA=0,70,140mg/d). Feeding trial lasted6weeks. The DMI was recorded weekly in three consecutive days. At the end of the trial, four lambs from each group were slaughtered, and duodenum and ileum mucosa were obtained from RNA abundance measurements of genes regulating feed intake. The result indicated that DMI was significantly higher (P<0.05) in the lambs fed140mg/d GABA than those of the control during the whole period. Compared with control, lambs fed140mg/d RP-GABA had higher mRNA abundance of GABA-B receptor (P<0.05) and lower mRNA abundance of CCK-2receptor (P<0.05) in duodenum mucosa. The results indicated that RP-GABA regulated dry matter intake by affecting mRNA abundances of GABA-B and CCK-2receptors in duodenum epithelia.In summary, coating material could be the key factor in stability of the RP-GABA products. Addition of GABA enhanced feed intake and then milk performance in both transition and early lactating cows, respectively. The optimal doses of GABA were1.2and0.6g/d for transition cow and early lactating cows, respectively. Regulatory effect in feed intake induced by GABA might be related with CCK metabolic pathway. |
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