Background: Appraisal of the effectiveness of supplementary mineral nutrition in grazing range cattle to promote growth and reproduction is lacking due to an inability of methods to measure cause and effect relationships, record variability of grazed diet mineral concentrations, evaluation of cattle presence at mineral feeder, measurement of shifting requirements due to changes in physiological stage and a lack of accurate mineral supplement intake quantification.
Methods and findings: This study evaluated cattle presence at mineral feeder, relative mineral intake and its association with calf Body Weight (BW) at birth and weaning, cow BW change and calving interval (d). Cross-bred cows grazed native range with access to mineral feeders containing 34% salt, 57% macro/microminerals, 9% distillers’ grains and 1% titanium (Ti) as titanium dioxide for sixteen months from August 2010 to November 2011. Motion activated cameras were used to record ear tags of 106 cross-bred cows as their heads approached the open range mineral tub. Mineral feeder tubs were placed near water sources to promote contact of cattle with mineral supply. Rectal fecal samples were collected at 1 or 2-months interval and were analyzed for Ti content. Filtered samples were transferred to 15 ml falcon tubes for Ti analysis using inductively-coupled plasma mass spectrometry analytical technique (USFS Bozeman Fish Technology Center, Bozeman, Montana, USA). It was assumed that fecal Ti was positively related to mineral consumption. Cows were assigned to one of four fecal Ti concentration clusters based on their mean Ti concentration: (1) low (3 to 5 ppm, n=23), (2) mid-low (5 to 6 ppm, n=36), (3) mid-high (6 to 7 ppm, n=26) and (4) high (7 to 11 ppm, n=21). Data were analyzed using Proc Mixed SAS (SAS Inst., Inc., Cary, NC) and a model including Ti cluster and cow age (2 to 11 years) as a covariate. The percent of cows at mineral tub each day differed (p<0.01) by season. In late growing season (July-October), 48 ± 3.9% of herd visited the tub daily compared to 31 ± 3.4% in fall and winter dormancy (November-March) and 27 ± 4.1% during spring growth (April-June). Average consumption based on amount of mineral fed was greatest (p<0.01) during forage dormancy and spring growth (53 ± 3.8 g hd-1 d-1) and lowest during late growing season (38 ± 3.5 g hd-1 d-1). Regardless of fecal Ti concentration, all groups had similar 2011 calf BW at birth (p<0.22) and weaning (p=0.89), cow BW change (2010-2011) p=0.71 and 2010 to 2011 and 2011 to 2012 calving interval (p=0.85). In addition, mean fecal Ti in 18 non-pregnant and 88 pregnant cows were 6.22 ppm and 5.95 ppm (p=0.68), indicating no differences in mineral consumption between non-pregnant and pregnant cows.
Conclusion: During the late growing season, cow activity at a mineral tub was highest but mineral disappearance from the tub was the lowest. Range in mean fecal Ti of individual cows represented a 3-fold divergence in Ti dilution indicating a magnitude difference in mineral consumption. If mineral consumption was a primary production limitation in the year of this study, then differences would be expected for the production traits evaluated influenced by predicted mineral intake.
Petersen MK, Muscha JM, Roberts AJ