Albornoz,Rodrigo_MSc_Short-term feed restriction in cattle-mitigating negative effects by altering the forage-to-concentrate ratio of the die_January_2013
The objective of this thesis was to evaluate the effects of altering the forage-to-concentrate ratio (F:C) of the diets fed prior-to and during a period of severe short-term feed restriction (FR) and the dietary F:C following FR on ruminal fermentation and short-chain fatty acid (SCFA) absorption. Twenty ruminally cannulated Angus × Hereford heifers were fed ad libitum either a high-forage diet (HF) with a F:C of 92:8 or a moderate-forage diet (MF) with a F:C of 60:40 during a 5-d baseline period (BASE), followed by 5-d of FR at 25% of their ad libitum intake (collectively represented as PRE). After exposure to FR, heifers were provided feed for ad libitum intake and the recovery was monitored for 3 consecutive weeks (REC1, REC2 and REC3; collectively denoted as POST), with one half of the HF and MF heifers remaining on the same diet, and the other half switched to the alternative diet. Dry matter intake (DMI) was measured daily and ruminal pH was recorded every 2 min. Ruminal fluid was collected on d 3 of BASE and FR, and on d 5 of each REC week. Ruminal SCFA absorption was assessed in vivo using the isolated washed reticulo-rumen technique on d 5 of BASE and FR and on d 7 of REC1 and REC3. Data were analyzed as a complete randomized block design to evaluate 1) the effects of FR (BASE vs. FR) when feeding a HF or a MF diet, and 2) the effects of the F:C of the diet fed PRE and the diet fed POST on the recovery from a period of short-term FR. With respect to the effect of the F:C of the diet fed PRE on the response to FR, diet × period interactions were detected for DMI (P = 0.030) and ruminal SCFA concentration (P = 0.025), respectively. The interactions were the result of higher DMI and numerically higher SCFA concentration for MF than HF during BASE, with a reduction observed for both during FR, although diet effects were no longer present during FR. Period effects (BASE vs. FR), but not diet effects (P > 0.05), were detected for mean ruminal pH (P < 0.001) and the total SCFA absorption rate (mmol/h; P = 0.038). During BASE, mean pH was lower (6.44 vs. 6.86) and the SCFA absorption rate was greater relative to FR (674.5 vs. 554.8 mmol/h). It can be concluded that FR had a negative impact on ruminal SCFA absorption, while altering the diet F:C does not mitigate these effects. With respect to the recovery response, PRE × POST and PRE × POST × period interactions were tested but were not significant, thus the interactions for the PRE × period and POST × period are emphasized and main effects of diet and period are presented when the interactions were not significant. Interactions (PRE × period) were detected for DMI (P = 0.045) and duration (amount of time pH < 5.5; P = 0.003). For heifers fed HF during PRE, DMI increased from REC1 to REC2, and from REC2 to REC3, while for heifers fed MF DMI did not differ among REC periods. Duration (amount of time pH < 5.5) was numerically higher during REC1 for heifers fed HF than MF PRE (191 vs. 98 min/d), with duration decreasing from REC1 to REC2 with no further change in REC3. Total ruminal SCFA concentration and absolute absorption rate were not influenced by the diet fed PRE or period (P > 0.05). There were POST × period interactions for DMI (P = 0.033) and duration (P < 0.001). Dry matter intake was maximized (10.1 vs. 8.4 kg/d) without a substantial increase in duration (14 vs. 275 min/d) during REC1 when heifers were fed HF relative to those fed MF during POST, without differences thereafter between treatments, but DMI increased from REC1 to REC2 and from REC2 to REC3. The duration that ruminal pH was < 5.5 decreased from REC1 to REC2, without differences between REC2 and REC3 (145, 29 and 46 min/d, respectively). Regardless of the diet fed POST and the week of REC, total ruminal SCFA concentration and absolute absorption were not affected (P > 0.05). It can be concluded that severe short-term FR had a negative impact on ruminal SCFA absorption regardless the diet fed prior-to and during FR. In addition, the dietary F:C affected the recovery response with a hastened recovery when heifers were fed a diet with a low F:C prior-to and during FR and a high F:C diet post FR, without any effects on SCFA absorption.
DegreeMaster of Science (M.Sc.)
DepartmentAnimal and Poultry Science
SupervisorPenner, Greg B.
CommitteeMutsvangwa, Tim; Beauchemin, Karen; McKinnon, John
Copyright DateJanuary 2013
short-chain fatty acid absorption