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The California Net Energy System (CNES) has been successfully used for many years to generate estimates of grazing animal energy requirements, supplemental needs, and energy value of grazed forage diets. Compared to pen feeding situations, validation of feed nutritive value estimates or animal performance projections are extremely difficult in grazing animals because many of the system inputs are constantly changing. A major difficulty in applying this or any energy accounting system in the field is acquiring accurate estimates of forage intake. We discuss the various equations available to estimate forage intake for grazing animals with emphasis on beef cows. Progress has been made in recent years although there remains substantial discrepancy among various equations, particularly in the upper range of forage digestibility. Validation work and further development is needed in this area. For lactating cows, our conclusion is that the adjustment of intake for milk production (0.2 kg increase in forage intake per kg of milk produced) needs to be increased to a minimum of 0.35. A particular challenge with the CNES for grazing beef cows is the dramatic interaction that can occur between genetic potential for production traits and nutrient availability. Examples from literature are provided and a case study is presented demonstrating that energy requirements are dynamic and depend on nutrients available in grazing systems. The CNES is a useful tool in grazing beef cattle management although there remains substantial opportunity and need to improve inputs and validate the system in grazing situations. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the impact of previous human interaction on the behavior of beef cows while they are being handled. To achieve this, 84 F-1 Angus x Brahman cows were randomly assigned to one of two human interaction treatments. The positive human-animal interaction group (P) was subjected to daily contact with a herdsman (on foot) for 15 minutes and was fed supplement by the herdsman. The control group (N) was checked daily and fed from a vehicle, with no direct human interaction. Each acclimation procedure was replicated in 2 pastures/herds (n = 16 to 26 cows in each herd). During routine processing times for these herds (d 0, 256, and 317), herds were gathered from their pastures and temperament was assessed. Chute and alley scores were assigned to individual animals by the same trained observer and ranged from 1 (calm) to 5 (aggressive). Chute exit velocity was also measured. Temperament variables were evaluated with ANOVA as a split plot with acclimation procedure in the whole plots and pasture as the whole-plot experimental unit, and processing time in the split plot. Neither human interaction (P = 0.99) nor time (P = 0.13) affected chute exit velocity. Chute score increased through time (P = 0.01) but was not affected by human interaction (P = 0.70). Alley score was not affected by human interaction (P = 0.32) or time (P = 0.81). Neither time nor the specific type of human acclimation we implemented affected cattle temperament, indicating other traits may be more important. Alternatively, different acclimation procedures may be more effective to improve cattle temperament. [ABSTRACT FROM AUTHOR]

New technologies have enabled autonomous measurement of intake and feeding behavior of pen-fed animals and this has piqued interest in utilizing similar technologies in grazing experiments. Various feeding systems are currently available, but individual supplementation and feeding experiments have been conducted for years using individual feeding stanchions, which are the lowest level of technology for measuring supplement intake. These experiments are laborious as they require animals to be trained and acclimated, gathered at each feeding, and sorted into individual stalls for supplementation--thereby disrupting the animals grazing activities. In the mid-1980s Calan Gate systems (American Calan; Northwood, NH) became popular in pasture supplementation experiments, but still have many of the same disadvantages. Newer, more automated systems, reduce labor and possibly have less disruption of the animal's grazing behavior, but are reliant on the animal's willingness to use the system and ability to access it when more dominant peers are present. Individuals also do not always follow the "averages"-based rules we often hold true and behave differently in groups. Recent research with automatic feeders show steers consumed average of 60% of the potential supplement with supplement intake CVs of 50 to 100%. These technologies lead many to question the paradigm of experimental units in experimental designs. The experimental unit is defined as the smallest independently assigned unit to which the treatment is applied. This definition of experimental unit is somewhat limiting when taken to the extreme, but still applies well for experiments utilizing individual animal feeding, regardless of the level of technology involved. In many cases where the aforementioned technologies are used, the individual animal can be both the observational and experimental unit. This symposia presentation will discuss attributes of different feeding options and the implications on study design, experimental power, and the designated experimental unit. [ABSTRACT FROM AUTHOR]

A 72-d trial was conducted to estimate the combined effect of forage allowance and a fiber-based energy supplement in stocker cattle grazing wheat. Eight pastures (2.7 to 5.1 ha) each contained seven test steers (initial BW = 210 ± 36 kg). Weekly, additional steers were stocked in each pasture in a put and take method to achieve forage allowance of either 2.5 or 5.5 kg forage DM / kg steer BW (4 pastures each). Two pastures in each forage allowance were fed daily with a supplement containing 50% wheat midds and 50% soybean hulls at the rate of 1.5 kg per steer. Forage mass was measured twice weekly using a calibrated rising plate meter. Cattle were weighed weekly on calibrated scales. Data were analyzed using linear regression with pasture as the experimental unit. Mean ADG was 1.36 kg/d. One pasture in the high forage allowance, non-supplemented treatment was removed because we were unable to maintain the designed forage allowance. The interaction of forage allowance and supplement was not significant (P = 0.37) for ADG, and supplementation did not affect ADG (P = 0.20), however increased forage allowance tended to improve ADG (P = 0.06, 0.21 kg ADG per kg forage allowance). To further investigate forage DMI, a 14-d trial began on day 36. Three of the seven test steers in each pasture were randomly chosen and administered 7 ± 0.1 g of TiO2 daily at 0700 as an external marker to estimate fecal output. Forage DMI (at an assumed 72% DM digestibility) averaged 2.1% of midpoint BW, below our expectation. Additional forage allowance tended to improve estimated forage DMI (P= 0.06), but supplement had minimal effect (P = 0.30). [ABSTRACT FROM AUTHOR]