Experiments were designed to assess the effects of energy and protein intake on metabolic function and reproductive efficiency in single and twin suckling beef cows and heifers. A role was proposed for endogenous opioid peptides in mediating the effects of photoperiod, suckling and nutrition on anterior pituitary hormone release, and tested with respect to nutrition. The first two experiments were designed to quantify the effects of pre- and post-partum energy and protein intake, on milk yield and composition, body tissue mobilisation, the post-partum anoestrous interval, and subsequent conception rates to artificial insemination and embryo transfer in single- and twin-suckling beef cows. Cows very quickly adjusted their metabolism and level of performance to be in line with their current level of energy and protein intake. Ovulation and the resumption of normal oestrous cycles occurred soon thereafter. The third experiment tested the hypothesis that post-partum energy and digestible undegradable protein (DUP) intake can influence hypothalamic opiodergic tone and the ability of the anterior pituitary to secrete luteinizing hormone (LH), prolactin and growth hormone in response to naloxone (an opioid receptor antagonist) challenge. Results indicated that high energy diets allowed cows to overcome the opioid mediated block on LH release and resume oestrous cyclicity earlier than cows on low energy diets. High levels of DUP increased the opioid mediated block on LH release. The final experiment examined the interactive effects of body condition and energy intake on hypothalamic opioidergic tone and pituitary responsiveness, in terms of LH release, when challenged with an exogenous source of gonadotrophin-releasing hormone (GnRH). Naloxone was unable to evoke consistent LH responses in this experiment but the LH response to GnRH was influenced by both body condition and energy intake. In conclusion opioid peptides may provide a means by which certain homeostatic regulators interface with homeorhetic hormones released from the anterior pituitary gland.

Doctor of Philosophy / Department of Animal Sciences and Industry / Jeffrey S. Stevenson / Four experiments were conducted in beef cows to determine factors that increased the probability of pregnancy per AI when cows are inseminated by appointment. Cows in all experiments were inseminated after a 7-d CO-Synch + CIDR program (100 μg GnRH [2 mL Factrel, Pfizer Animal Health, Whitehouse Station, NJ] 7 d before 25 mg PGF₂[subscript]α [d 0; 5 mL Lutalyse; Pfizer Animal Health]). Experiment 1 compared 1 vs. 2 inseminations and GnRH injection times at 60 and 75 h after the CO-Synch + CIDR program. Delaying AI until 75 h, according to interpretation of estrus-detection patches, for cows not in estrus by 60 h after CIDR insert removal increased (P < 0.05) pregnancy risk (PR) compared with cows not in estrus and inseminated at 60 h (51.4 vs. 41.7%), respectively. The necessity of GnRH injection concurrent with AI was tested in experiment 2. Cows displaying estrus by 65 h that were injected with GnRH had similar PR to cows in estrus and not treated with GnRH (61.9 vs. 60.4%), respectively. Cows in experiment 2 that did not display estrus, but were treated with a GnRH injection at 65 h and then inseminated at 84 h after CIDR insert removal had increased PR compared with similar cows not treated with GnRH (33.4 vs. 15.0%; P < 0.01), respectively. Experiments 3 and 4 were observational studies conducted to determine if blood metabolites glucose and beta-hydroxy butyrate (BHB experiment 3), or physical body and blood metabolites, (glucose, BHB, non-esterified fatty acids [NEFA], blood urea nitrogen [BUN], body weight, rump fat [RF], or BCS; experiment 4) were indicative of future reproductive success in suckled beef cows enrolled in a timed AI program. In experiment 3, plasma glucose concentration 10 d before AI was lesser (P = 0.01; 52.2 vs. 56.9 mg/dL) and serum BHB concentration was lesser (P < 0.01) in cows that became pregnant 35 d after timed AI than for cows that did not become pregnant (600 vs. 690 μM), respectively. Experiment 4 identified relationships between indicators and reproductive success including the finding that serum NEFA concentration 2 to 4 wk before AI is negatively correlated (P < 0.05) with PR to AI.

Two experiments were conducted to determine the effects of grazing stockpiled perennial forage in field paddocks relative to feeding similar quality round bale hay in drylot pens on rumen degradation characteristics of forage; beef cow performance, cow reproductive efficiency, estimated dry matter intake and forage utilization, forage yield and quality, soil nutrients and system costs. Winter feeding systems were (i) stockpiled perennial forage (TDN = 58.9%; CP = 8.5%) grazing (SPF) and (ii) drylot feeding (DL) of round bale hay (TDN = 57.9%; CP = 8.4%). Experiment I was an in situ study, where five Hereford heifers (398 ± 14 kg) fitted with rumen cannulae were fed a grass hay (DM = 93.2%; TDN = 50.8%; CP = 9.8%; NDF = 66.2%) diet. In situ degradability of both stockpiled forage (SPF) and round bale hay (BH) samples collected at start (October) and end (December) of the field study were determined. The soluble fraction (S) of DM was greater (P = 0.01) in SPF October forage compared to SPF December, BH October and BH December forages. The potentially degradable fraction (D) of CP was lowest (P = 0.04) in BH December forage than in SPF October, SPF December and BH October forages suggesting that hay quality declined more rapidly than stockpiled forage and method of preservation may have affected overall hay quality. Furthermore, D fraction of both ADF and NDF was higher in SPF samples suggesting stockpiled forage may be more digestible than hay. However, the D fraction of NDF in both SPF and BH forages declined with later sampling date possibly due to effect of weathering and leaf loss. In Experiment II, 6, 4-ha paddocks consisting of meadow bromegrass (Bromus riparius Rehm) and alfalfa (Medicago sativa), were randomly assigned to 1 of 2 replicated (n = 3) winter feeding systems. In this study 58 dry pregnant (120 ± 16 d) Angus cows (675 kg ± 51 kg), stratified by body weight (BW; corrected for conceptus gain), were allocated to either the SPF or DL systems. Cows in winter feeding systems were provided additional energy supplement (rolled barley) (TDN = 86.4%; CP = 12.4%) depending on environmental conditions to maintain body condition, with no weight gain above that of conceptus growth. Dry matter intake (DMI) and forage utilization were estimated using the herbage weight disappearance method. The effects of winter feeding systems on soil nutrients were determined the following spring after winter grazing. Forage yield in DL (4683 ± 495 kg ha-1) and SPF (4032 ± 495 kg ha-1) systems was not different (P = 0.18) between treatments. However, forage utilization was lower (P < 0.01) in SPF (83.5%) than the DL (94.4%) system, signifying lower accessibility to stockpiled forage due to snow depth, lower temperatures, freezing rain and wind. Cows in the SPF system had higher forage DMI (P = 0.04) and supplementation intake (P < 0.01) compared to cows in drylot pens likely a combined effect of effective ambient temperatures below the lower critical temperature (LCT) during the grazing period and the higher potentially digestible fraction of neutral detergent fiber in stockpiled forage than hay. Cow BW change, average daily gain, rib fat change and rump fat change were not different (P > 0.05) between winter feeding systems. Reproductive performance of beef cows was not affected (P > 0.05) by either winter feeding methods as cows in both systems maintained body condition score (BCS) at 2.5 to 3.0 throughout the study. Average total production cost was 19% lower in SPF system compared to DL system. In conclusion, the rumen degradation characteristics of stockpiled perennial forages focused in this study support the utilization these forages in a winter feeding system to meet the nutrient requirements of dry beef cows in early to mid-gestation. It may be cost effective to manage beef cows in field grazing of stockpiled perennial forages in western Canada, without any negative impact on beef cow performance or reproductive efficiency.

Doctor of Philosophy / Department of Animal Sciences and Industry / KC Olson / The objective of this series of studies was to develop and improve methods of production in cow/calf operations of the Great Plains. Ultrasound measures of longissimus muscle depth (LMD) and intramuscular fat (IMF) of Angus × heifers were used to predict lifetime cow productivity. IMF and LMD were categorized into high, medium, and low groups (IMFG and LMDG, respectively). Cows in the high and medium LMDG had greater (P < 0.05) pregnancy rates than cows in the low LMDG. Calf BW at weaning increased (P < 0.05) as dam IMF increased. Angus crossbred cows grazing native range were used to evaluate the effects of pre-partum ruminally-protected choline (RPC) supplementation on postpartum beef cow and calf performance. Under the conditions of our study, RPC supplementation had minimal (P > 0.05) effects on pregnancy rates and performance of beef cows and calves. Lactating crossbred cows with calves and non-pregnant, non-lactating Boer-cross nannies were used to evaluate the effects of co-grazing on herbivory patterns and animal performance while grazing native tallgrass rangeland infested heavily by sericea lespedeza (SL). The proportion of individual SL plants that had been grazed at the end of the trial was greater (P < 0.01) in co-grazed pastures than in single-species pastures. Grazing cows and goats in combination increased (P < 0.01) grazing pressure on SL without negatively affecting beef cow performance, beef calf performance, or residual forage biomass. Angus × cows and heifers grazing native range were used to evaluate the effects of pre-partum corn steep liquor supplementation on postpartum beef cow and calf performance. Under the conditions of our study, CSL supplementation did not generally promote beef cow and calf performance that was equivalent to supplementation with an isonitrogenous, dry, corn-soy alternative. Cow calf pairs were used to evaluate the effects of grazing system (GS) and stocking rate (SR) on cow and calf performance. Late season rest-rotation (LSRR) was compared with continuous (CONT) grazing at low, moderate, and high SR. Under the conditions of our study, CONT produced consistently better (P < 0.01) late-season cow and calf performance than LSRR. Season-long effects of SR on animal performance were minimal; moreover, GS and SR treatments produced equivalent pregnancy rates.

The objectives of the current study were: 1) to examine serum bPAG concentration during pregnancy, and in the post-partum period in relation to the overall nutritional and metabolic status and post-partum anoestrous period; 2) to investigate bPAG decay models for postulating distribution and metabolism of bPAG in the blood circulation using half-life (t1/2) and to compare the t1/2 values between breeds and nutritional treatments for the clearance of bPAG; 3) to examine the suitability of the radioimmunoassay (RIA) for measuring bPAG in urine, saliva and milk, to investigate temporal relationships between bPAG in these fluids and that in the serum, and to assess the potential of bPAG in these fluids for pregnancy diagnosis in cows. Estimation of total bPAG disappearance from plasma per day during week 1 post-partum did not differ between the breeds. Urinary bPAG, over the same period of time, was lower for Welsh Black than Simmental and Charolais cows (0.45 vs 0.53 and 0.59 nmol (s.e.d 0.03) p<0.05) but not for Aberdeen Angus cows (0.48 nmol); bPAG in saliva was lower for Welsh Black than Charolais and Aberdeen Angus cows (1.65 vs 2.42 and 2.49 nmol (s.e.d 0.11) p<0.05) but not for Simmental cows (1.44 nmol/1), and bPAG measured in milk (whole) was lower for Charolais than Simmental cows (0.26 vs 0.47 nmol (s.e.d 0.06) p<0.05) but not for Aberdeen Angus (0.38 nmol/1) and Welsh Black cows (0.37 nmol/1). Total body elimination of bPAG in urine, saliva and milk accounted only for 5.28 % of the total plasma bPAG. Total body elimination of bPAG in urine, saliva and milk accounted for only 5.28 % of the total plasma bPAG. The remaining 94.72 % of bPAG may have been metabolished and was undetectable by the current RIA technique. A theoretical assessment for potential use of bPAG RIA for pregnancy diagnosis using urine, saliva and milk showed that the minimum detection limits of measuring bPAG in these fluids were reached and / or exceeded by Day 200 of gestation, or later. Consequently, assay of bPAG in these fluids for early pregnancy diagnosis would not be appropriate unless the sensitivity of the assays is improved considerably, or prior assay sample extraction/concentration is carried out.

The present investigation was designed to investigate the use of blessed thistle (Cnicus benedictus) in amelioration of fescue toxicosis in beef cattle. Twenty-seven crossbred Angus cows were blocked by age and weight into groups of three. Each group (n=9) was then randomly assigned to one of three dietary treatments: endophyte-free (EF), endophyte-infected (EI), or endophyte-infected with addition of cut and stemmed blessed thistle (EIBT). Each group was also randomly assigned to one of three 29-day replicates. Parameters measured during this trial included: urinary ergot alkaloid concentration (ng ergot alkaloids/mg creatinine), body weight (kg), rectal temperature (°C), serum progesterone (ng/ml), and serum prolactin (ng/ml). No effect of treatment (P>0.05) was detected in any of these parameters. A treatment x time interaction (P<0.0001) was observed for progesterone concentrations, likely a result of estrous cyclicity of cows. Results of this study suggest that we were unsuccessful in inducing fescue toxicity in test subjects assigned to EI and EIBT treatments. Minimal dietary ergovaline (1.72 μg kg-1) and cool ambient temperatures (-6.7°C to 23.3°C) likely contributed to this inability. Data from this research do suggest, however, that C. benedictus can be successfully incorporated into cattle diets. Further research will need to be performed to fully elucidate what, if any, benefits blessed thistle can have in the treatment of fescue toxicity.

Two experiments were conducted at the University of Kentucky, Eden Shale Farm, Owenton, KY to evaluate the use of MTB-100TM (Alltech, Inc., Nicholasville, KY) to alleviate the symptoms of fescue toxicity when lactating Angus x Beefmaster cows and their calves grazed endophyte-infected KY-31 tall fescue. Experiment 1 provided a carbohydrate based toxin adsorbent, MTB-100TM, ad libitum in a commercial mineral supplement to project a daily consumption rate of 0, 20 or 40 g of MTB-100TM per cow. Cows were weighed, assigned a body condition score (BCS) and hair coat score (HC), rectal temperatures were recorded and fecal grab samples were taken for ergovaline (EV) and lysergic acid (LA) analysis every 35 days for three grazing seasons (May to September). Calves were also weighed and assigned a HC score. Although MTB-100TM did not improve cow or calf performance, cows older than 4 years and those with greater Beefmaster breeding exhibited a higher tolerance to fescue toxicity than 2 and 3-yr-olds and cows with greater Angus breeding. Experiment 2 was conducted to evaluate the response of lactating beef cows and their calves to strategic supplementation with MTB-100TM. MTB-100TM was mixed with a complete mineral so daily intake was projected to be 0 or 20 g/cow. The experimental period extended from May 5 to October 2 and was divided into 3 strategic periods: P1 = May 5 to July 5; P2 = July 5 to August 31; P3 = August 31 to October 2. Treatments were either 0 or 20 g•cow-1•d-1 MTB-100TM within a period (Treatment 1 = 0, 0, 0; Treatment 2 = 20, 0, 20; Treatment 3 = 0, 20, 0; Treatment 4 = 20, 20, 0; and Treatment 5 = 20, 20, 20). Cow and calf performance was measured the same as Exp. 1, but every 21 days. Supplementation early in the grazing season tended to improve cow weight gain and body condition; however, there was no effect on calf performance. Fecal output of EV and LA did not increase in either experiment with supplementation. In conclusion, strategically invoked MTB-100TM consumption can increase performance of cows grazing endophyte-infected tall fescue forage.

Master of Science / Department of Animal Sciences and Industry / John Jaeger / Cattle grazing dormant native range (< 7% crude protein; CP) require supplementation of additional protein to sustain body weight (BW) and body condition score (BCS). Daily delivery of these supplements is an economic burden to cattle producers faced with challenging economic circumstances. Supplementing cows infrequently (as little as once/week) has produced equivalent BW and BCS changes compared to daily delivery. Dried distiller’s grains with solubles (DDGS) provides more ruminally-undegradable protein (RUP; 50-60%) compared to traditional oilseed-meal supplements (i.e. soybean meal) that are >50% ruminally-degradable protein (RDP). Therefore, our objective was to evaluate the effects of supplementation frequency on performance, reproductive success, eating behavior, and subsequent calf performance of spring-calving cows supplemented with DDGS. No differences in ending BW (P = 0.69) and BCS (P = 0.49), or changes in BW and BCS over the supplementation period (P = 0.82 and 0.70, respectively) were observed among cows supplemented every d, every 3 d, or every 6 d. Calf BW at birth, weaning weight (WW), and average daily gain (ADG) were similar among treatments (P = 0.19, 0.12, and 0.10, respectively). First-service conception rate (FSCR) and final pregnancy rate (PR) were also not affected by supplementation frequency (P = 0.62 and 0.76, respectively). The development of replacement heifers is a large expense for cow-calf producers. Improved breeding and heifer development strategies aimed at ensuring the success of replacement females have been developed but reproductive failure still remains a problem. The stress associated with breeding and handling procedures may decrease reproductive success. Therefore, the objective was to determine if intramuscular administration of flunixin meglumine (1.1 mg/kg BW) 14 days post-breeding would improve FSCR and PR in non-transported replacement heifers. Under the conditions of our study, flunixin meglumine did not improve (P = 0.87) first service conception rate above that of control heifers (41.2% and 42.3%, respectively). Final pregnancy rate also was not different between treatments and averaged 81.8% (P = 0.40).

Three experiments were conducted to determine the effects of supplementing wheat-based dry distillers grains with solubles (DDGS) on cow performance, forage utilization, and production costs. In the first two experiments, 48 dry, pregnant Black Angus cows (mean BW±SD; 598.2±4.2 kg) stratified by body weight (BW) and days pregnant were allocated randomly to one of three replicated (n=2) treatments. Cows were managed on stockpiled crested wheatgrass pasture (TDN=49.0, CP=7.3 (% DM)) in experiment one (EXP 1) and barley straw-chaff residue (TDN=45.4, CP=8.6 (% DM)) in experiment two (EXP 2). EXP 1 supplement treatments were (1) 100% DDGS (70:30 wheat:corn blend; DDGS); (2) 100% commercial supplement (COMM); or (3) control no supplement (CONT). EXP 2 supplement treatments were (1) 100% DDGS (70:30 wheat:corn blend; DDGS); (2) 50% DDGS + 50% rolled barley (50:50); or (3) 100% rolled barley grain (control; BARL). Forage utilization was measured for both trials using the herbage weight disappearance method. Cow BW, body condition score (BCS), and rib and rump fat were measured at the start and end of trial and cow BW was corrected for conceptus gain based on calving data. There was no effect (P > 0.05) of treatment on forage utilization in either experiment. In EXP 1, cow performance was not affected (P > 0.05) by supplement strategy. In EXP 2, BW change was 11.3, 6.8, and -6.5 (P < 0.01) for DDGS, 50:50, and BARL, respectively. Because forage utilization was not affected, the difference in cow BW was the result of supplement type. Costs per cow per day in EXP 1 were $0.66, $0.68, and $0.60 for DDGS, COMM, and CONT, respectively. In EXP 2, costs per cow per day were $0.79, $0.80, and $0.80 for DDGS, 50:50, and BARL treatments, respectively.<p> In experiment three (EXP 3), four ruminally cannulated beef heifers were individually fed a basal ration of 75% ground barley straw and 25% ground grass hay (TDN=46.3, CP=7.5 (% DM)). Heifers were supplemented with either (1) DDGS (70:30 wheat:corn blend; DDGS); (2) commercial range pellet (COMM); (3) barley grain and canola meal (BAR+CM); or (4) control no supplement (CONT). Forage intake, apparent total tract digestibility, and passage rate; rumen fermentation parameters; and the rate and extent of forage degradation were measured. Forage intake, passage rate, and apparent total tract digestibility of DM, NDF, and ADF were not affected (P > 0.41) by treatment. Apparent total tract digestibility of CP was increased (P = 0.02) by supplementation, but was not different between DDGS, COMM, and BAR+CM treatments. Ruminal pH was not affected (P = 0.20) by treatment diet, but rumen ammonia-N was increased (P < 0.01) by supplementation. The potentially degradable and undegradable forage fractions were affected (P < 0.02) by supplementation, reducing the extent of forage degradation. Also, there was a tendency (P = 0.06) for the rate of forage DM degradation to increase when supplements were fed. The results of these experiments indicate that wheat-based DDGS can be used as a supplement for beef cows consuming forages with similar or greater effects compared to a commercial pellet and barley grain. DDGS had similar effects on rumen metabolism as the commercial range pellet or barley grain and canola meal, suggesting DDGS can be substituted on a unit basis with these supplements. As such, the inclusion of wheat-based DDGS as a supplement for beef cows will depend on the initial price of the supplement.

Three experiments were conducted to determine the effects of supplementing wheat-based dry distillers grains with solubles (DDGS) on cow performance, forage utilization, and production costs. In the first two experiments, 48 dry, pregnant Black Angus cows (mean BW±SD; 598.2±4.2 kg) stratified by body weight (BW) and days pregnant were allocated randomly to one of three replicated (n=2) treatments. Cows were managed on stockpiled crested wheatgrass pasture (TDN=49.0, CP=7.3 (% DM)) in experiment one (EXP 1) and barley straw-chaff residue (TDN=45.4, CP=8.6 (% DM)) in experiment two (EXP 2). EXP 1 supplement treatments were (1) 100% DDGS (70:30 wheat:corn blend; DDGS); (2) 100% commercial supplement (COMM); or (3) control no supplement (CONT). EXP 2 supplement treatments were (1) 100% DDGS (70:30 wheat:corn blend; DDGS); (2) 50% DDGS + 50% rolled barley (50:50); or (3) 100% rolled barley grain (control; BARL). Forage utilization was measured for both trials using the herbage weight disappearance method. Cow BW, body condition score (BCS), and rib and rump fat were measured at the start and end of trial and cow BW was corrected for conceptus gain based on calving data. There was no effect (P > 0.05) of treatment on forage utilization in either experiment. In EXP 1, cow performance was not affected (P > 0.05) by supplement strategy. In EXP 2, BW change was 11.3, 6.8, and -6.5 (P < 0.01) for DDGS, 50:50, and BARL, respectively. Because forage utilization was not affected, the difference in cow BW was the result of supplement type. Costs per cow per day in EXP 1 were $0.66, $0.68, and $0.60 for DDGS, COMM, and CONT, respectively. In EXP 2, costs per cow per day were $0.79, $0.80, and $0.80 for DDGS, 50:50, and BARL treatments, respectively.<p> In experiment three (EXP 3), four ruminally cannulated beef heifers were individually fed a basal ration of 75% ground barley straw and 25% ground grass hay (TDN=46.3, CP=7.5 (% DM)). Heifers were supplemented with either (1) DDGS (70:30 wheat:corn blend; DDGS); (2) commercial range pellet (COMM); (3) barley grain and canola meal (BAR+CM); or (4) control no supplement (CONT). Forage intake, apparent total tract digestibility, and passage rate; rumen fermentation parameters; and the rate and extent of forage degradation were measured. Forage intake, passage rate, and apparent total tract digestibility of DM, NDF, and ADF were not affected (P > 0.41) by treatment. Apparent total tract digestibility of CP was increased (P = 0.02) by supplementation, but was not different between DDGS, COMM, and BAR+CM treatments. Ruminal pH was not affected (P = 0.20) by treatment diet, but rumen ammonia-N was increased (P < 0.01) by supplementation. The potentially degradable and undegradable forage fractions were affected (P < 0.02) by supplementation, reducing the extent of forage degradation. Also, there was a tendency (P = 0.06) for the rate of forage DM degradation to increase when supplements were fed. The results of these experiments indicate that wheat-based DDGS can be used as a supplement for beef cows consuming forages with similar or greater effects compared to a commercial pellet and barley grain. DDGS had similar effects on rumen metabolism as the commercial range pellet or barley grain and canola meal, suggesting DDGS can be substituted on a unit basis with these supplements. As such, the inclusion of wheat-based DDGS as a supplement for beef cows will depend on the initial price of the supplement.