Brood Cow Performance In Western North Dakota: Drylot Phase

By

D.G. Landblom and J.L. Nelson

Introduction: Calf weaning weight, nutrient requirements of the cow and the overall cost of production are parameters affected by a cow’s level of milk production, body condition, and mature body weight. Several investigations have been conducted to measure the interrelationship of cow size, maintenance requirements and calf weaning weight. They clearly show that energy requirements for maintenance are dependent on cow weight, and that as mature cow weight increases calf weaning weight also increases (Klosterman et al., 1968; Urick et al., 1971; Jeffrey and Berg, 1972; Miguel et al., 1972; Benyshek and Marlowe, 1973; Turner et al., 1974, NRC, 1984; Rode and Bowden, 1987).

Weaning weight can be raised by increasing mature body weight, increasing milking ability, or through a combination of both factors. Although selection for increased milk production among beef breeds results in heavier calves at weaning, infusing dairy blood into the beef herd is a more rapid method for increasing milk production (Cundiff, 1970). However, it is also associated with poorer reproductive performance when post partum energy levels are inadequate (McGinty and Frerichs, 1971; Halloway et al., 1975, and Wyatt et al., 1977). Rahnfeld and co-workers, in an evaluation of breed crosses maintained under two environments, reported that cows having the greatest milk yield were also identified as having below average weight of calf weaned per year. The reduction reported was due to reduced conception rates, high calf mortality and high cow losses during wintering. In their study, cows reared with insufficient energy intake sacrificed themselves to feed their calves. Loss of body condition put conception rates and winter survival in jeopardy.

Lactation status not only affects maintenance energy requirements, which are higher for cows of high milk production potential per unit of body weight than cows with low milk production potential (Ferrell and Jenkins, 1982), but it also increases forage intake of free ranging beef cows. Kronberg et al., (1986) found that the forage intake of lactating Hereford and Simmental x Hereford cross cows was 23% and 39% more, respectively, than their non-lactating counterparts.

Environmental differences under which beef cattle are raised in North Dakota vary widely from year to year, and within each year. In addition to dealing with environmental differences, cattlemen have a number of genetic options to choose from when deciding which genetic combination is best suited to their particular situation. The challenge for cattlemen therefore, is matching the genetic options available to them to the feed resources on their farms and ranches. This project is designed to help cattlemen in the decision making process, when evaluating cattle with varying production characteristics, by documenting the feed energy inputs necessary for cows with varying body weight and milking ability to reproduce and over winter successfully. Within the investigation there are three major relationships of importance: 1) the relationship between nutrition and reproduction, 2) the relationship between nutrition and total beef production, and 3) the relationship between grazing intensity and its affect on species composition, plant density change and overall carrying capacity.

The project is divided into two phases. Phase I is the drylot period when cows are confined and fed harvested feeds. Phase II is the grazing period . For the purpose of this progress report, only the drylot data will be reported and related to weaning weight.

Cow breed combinations being used to document energy inputs for western North Dakota were selected according to their expected mature body weight and milking ability, and are characterized as being light, medium and heavy for body weight, and low, medium and high for milking ability. The Hereford breed serves as the foundation and control breed and is characterized as being of medium body weight and low for milking production. Developed from the Hereford breed, the other breed combinations and categories are shown below:

Procedure: In 1986, the initial breed groups were fed long crested wheatgrass hay ad libitum and one pound of dry rolled barley per head daily during the gestation phase. As each cow calved she and her calf were weighed and transferred to postcalving lots where they were allowed free choice access to the complete mixed lactation ration shown in table 1. On May 21^st the groups were moved to crested wheatgrass pasture, and then exposed to fertile Charolais bulls on June 1^st. The breeding season was completed on July 31^st.

In 1987, the cows grazed crop aftermath until December 14, 1986 when they were moved into drylot and started on the silage based gestation rations shown in table 2. The groups were maintained on the rations for a one week adjustment period before being weighed on two consecutive days. Weights from the two consecutive weighings were averaged and the gestation phase was started on December 22, 1986. As each cow calved, she and her calf were weighed and transferred to separate cow lots reserved for each breed after calving, and started on the complete mixed lactation ration shown in table 2. The groups were maintained on these rations until they were turned out on crested wheatgrass spring pasture April 30, 1987. The previous year, 30 percent of the MS x A x H cows were open at the end of the breeding season. Therefore, in 1987 eight pounds of dry rolled barley was fed per head during the first heat cycle of breeding to the higher lactating Milking Shorthorn and Simmental cross cow groups. Fertility tested Charolais bulls were with the cow groups from June 1^st to August 1^st.

In 1988, the groups were handled in much the same way as in 1987, but didn’t graze crop aftermath as long. They were adjusted to the silage based gestation rations shown in table 3, and weighed on trial December 15, 1987. A longer drylot lactation period was needed in 1988 because of drought. Below normal spring precipitation and above normal temperatures combined to reduce crested wheatgrass growth substantially. The cow groups were turned out on crested wheatgrass on May 27, 1988 when suitable growth was attained. Feeding of eight groups (MS x A x H and S x H) began on May 27^th also. Fertility tested Charolais bulls were with all groups from June 1^st until August 15^th. The breeding season was extended two additional weeks because of the prolonged high temperatures experienced during June and July.

In 1989, drought conditions also shortened crop aftermath grazing. The cow groups were adjusted to the drylot rations shown in table 4, and weighed on trial November 10, 1988, after two consecutive weighings. Spring turnout on crested wheatgrass and the feeding of barley flushing supplement to the two highest lactating groups (SxH and MSxAxH) both occurred on May 25, 1989. As in previous years, fertility tested Charolais bulls were put with the cows on June 1^st and removed on August 15, 1989.

The experiment began in 1986 with an unequal number of cows in each breed group that were bred to Charolais. In all subsequent years the herds have been maintained at ten cows. Replacements for cows that have had to be removed from the study have been limited. Replacements are being made at two specific times during the production year. Cows that lose calves anytime before the start of the breeding season on June 1^st are replaced with a comparable pair from a reserve gene pool. Those cows that are examined for pregnancy and identified as open at weaning are replaced with a comparable bred cow from the reserve pool when the winter feeding period is started.

Dry matter intake during gestation has been regulated based on body weight measurements taken biweekly. The breed groups are fed to gain approximately two pounds daily during the last trimester of pregnancy so that they will have a net gain after calving ranging from .2 and .4 tenths of a pound per day. The (H) and (A x H) groups are fed 22 pounds of dry matter as a basal ration, and the (MS x A x H) and (S x H) groups are fed 24 pounds of dry matter as a basal ration. Adjustments to the basal dry matter intake levels are made upward or downward based upon body weight changes at biweekly weighing, and are further adjusted for cold weather according to the following schedule: 15^oF (no adjustment), 0^oF (+9%), -15^oF (+18%), and -30^oF (+27%).

In this study, energy input is being measured in megacalories per pound of calf weaned per exposed cow and is obtained by charting the total calculated digestible energy consumed during gestation and lactation in drylot against the pounds of calf weaned from all exposed cows. Additional measurements include: 1) gestation and lactation body weight changes, 2) gestation and lactation dry matter feed consumption, 3) wintering economics, and 4) milking ability estimates at selected dates during the grazing season.

Milk production is estimated using the weigh-suckle-weigh method (Neville, 1962). The estimates are being made approximately mid June, late August, and late October of each year.

Statistical analysis was conducted with MSUSTAT (version 4.10).

Results and Discussion: Four of seven drylot wintering cycles scheduled for this long term investigation have been completed. Drylot wintering begins in mid December after the cow groups have completed grazing crop aftermath, and continues until approximately mid May when the breed groups are turned out on crested wheatgrass pasture. Starting and completion dates have varied each spring and fall in response to seasonal precipitation ands its affect on grazable forage. The summer grazing period on native range begins the third week of June each year, and is completed when pastures are sufficiently grazed based on clipping appraisals.

The Nutrient Requirements of Beef Cattle (1984) handbook currently recommends that dry pregnant mature beef cows weighing approximately 1100 pounds should consume 21.0 pounds of dry matter that contains 53.2% TDN, and it further recommends that 1200 pounds cows in the same stage of pregnancy consume 22.3 pounds of dry matter containing 52.9% TDN. Our past winter feeding experience indicates that NRC recommendations need to be adjusted upward approximately 10% to account for the more harsh environment of southwestern North Dakota. Rahnfeld and co-workers found in their work with ten breed crosses that NRC feeding standards needed to be adjusted upward an average 17% to account for the environmental differences encountered in Canada. In our study, we have found that each cow group has required feeding of a different level of dry matter in order to maintain body weight at or near the projected levels. The wintering and lactation rations fed are shown in tables 1, 2, 3 and 4, and a comparison of the levels of dry matter fed versus NRC recommendations is shown in table 5. The heaviest body weight (SxH) and the lightest body weight (MSxAxH) groups have been fed 8.2% and 13.9% above NRC standards, respectively, and experienced a slight weight improvement up to calving, as shown in table 6. The moderate body weight groups (H and AxH), were fed 9.1% and 5.7% above NRC standards, respectively, but had a slight weight loss up to calving. The values used appear to be sufficient for wintering provided that feed levels after calving contain adequate energy for lactation and body weight gain. Rations used during the short lactation period after calving, but before turnout on crested wheatgrass, have provided adequate energy for lactation and body weight gain. Gains for each body weight group are as follows: light weight (MSxAxH) .94, moderate weight (H) 1.13, moderate weight (AxH) .89, and heavy weight (SxH) .70. Feed intake to produce these gains during the short period between calving and turnout on spring pasture appears to be one of the keys to reproductive success.

Drylot costs for wintering and lactation are also shown in table 6. When combined, the total average wintering costs were as follows: light weight (MSxAxH) $171.11, moderate weight (H) $154.32, moderate weight (AxH) $165.00 and heavy weight (SxH) $175.78.

Table 7 contains a four year production summary. The highest milking ability groups (MSxAxH and SxH) had longer postpartum intervals, but the difference between them and the other two lower milking groups (H and AxH) were not significant.

Milking ability had a positive (P<.01) effect on weaning weight. The highest milking group (MSxAxH) produced calves that weighed 642.8 pounds, which was significantly heavier than the lowest milking ability group (H) that weaned calves averaging 578.2 pounds. Pounds of calf weaned per cow exposed is a measurement in part of reproductive failure. Therefore, the significant advantage measured for weaning weight is lost when reproduction is taken into account. Pounds of calf weaned per cow exposed to date are as follows: light weight (MSxAxH) 587.1 pounds, moderate weight (H) 547.8 pounds, moderate weight (AxH) 578.1 and heavy weight 588.7 pounds.

Feed costs per pound of calf weaned per cow exposed, which are also shown in table 7, were relatively close. Costs incurred to date per pound of calf weaned per cow exposed are $.2813 (H), $.2914 (MSxAxH), $.2829 (AxH) and $.2985 (SxH). Expressing these costs in term of net return over feed and processing makes the differences easier to understand. Table 8 shows a partial economic analysis in which feed and processing charges have been deducted from the gross returns per cow exposed. The moderate weight/moderate milking ability (AxH) group returned most the net dollars of $13,938.72. This was $402.22 more than the heavy weight/moderate milking ability (SxH) group that netted a total of $13,536.50. The light weight/high milking ability (MSxAxH) group returned $29.08 less, and the moderate weight/low milking ability (H) group returned $310.98 less than the highest returning (AxH) group.

Summary: There are three more production years and grazing data to be incorporated into this project before it is finalized. It is apparent, however, that while the cows used in this study represent only a small number of breeds and combinations available to select from in the beef industry, their diversity in terms of body weight and milking ability are manageable within the environment of southwestern North Dakota.

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