Increasing evidence suggests that climate change is increasing the likelihood of co-occurring periods of
precipitation deficit and warm temperatures over the next century. Maintaining ecosystem function and
agricultural productivity on rangelands during increasingly intense and frequent periods of drought
presents scientific, economic, and social challenges. Rangeland livestock producers are often the first to
feel the impacts of drought; these impacts can be especially pronounced on California’s annual
rangelands (where the majority of precipitation and forage growth occurs in fall, winter and spring).
Structured interviews of ranchers conducted prior to and following the conclusion of California’s 2012-
2015 drought have highlighted the proactive and reactive strategies employed by ranchers to mitigate
drought effects. While early weaning is a strategy used by significant numbers of ranchers, very little
research has been conducted in annual rangeland systems to determine whether such a strategy is
beneficial economically or ecologically. The broad goal of this project is to quantify the costs and
benefits of early weaning as a drought management strategy for fall-calving cow-calf operations in
California. We will quantify the influence of early weaning on forage resources, evaluate influence on
cow and calf performance, and analyze the economic tradeoffs associated with early weaning compared
to traditional weaning strategies.
The overarching goal of this project is to work with fall-calving cow/calf ranchers to understand
the potential net economic and environmental benefits of early weaning as a drought
management strategy. Specific objectives include:
1. Quantify the influence of early weaning on cow and calf performance, pasture utilization, soil
protection, and plant biodiversity and examine how year-to-year variation in precipitation
influences early weaning effects.
2. Develop decision tools to help producers evaluate the economic and ecological tradeoffs
associated with early weaning compared with traditional weaning strategies using data
collected in objective #1.
3. Create and deliver a basic decision support guide that synthesizes the economic and ecological
tradeoffs with producer expert input to allow producers to determine how and when early
weaning may work as a drought adaptation practice for a particular enterprise.
We are in the initial stages of this project. To date, we have held a producer steering committee meeting, developed a detailed project schedule, and collected initial body condition scores on the cows. This winter, we will read forage transects and plots, and wean the first calves (in early March). Normal weaning will occur in late May or early June.
2019 marked our first full year of data collection and experimental treatment:
- February 2019: Establish forage production monitoring sites. Assign cattle to early weaning and traditional weaning treatment groups.
- March 19, 2019: Wean calves in early weaning group. Collect individual weights on weaned calves. Collect body condition scores on all cows (early weaning and traditional).
- March 26, 2019: Cattle placed on paired treatment pastures (3 early weaning pastures and 3 traditional pastures).
- May 28-June 1, 2019: Forage samples collected at 15 sites in 6 pastures. Measurements included total forage production, forage harvested, species richness (grazed and ungrazed), percent bare ground (grazed and ungrazed), and percent invasive plants (grazed and ungrazed).
- May 30, 2019: Wean calves in traditional weaning group. Collect individual weights on early weaned and traditional weaned calves. Collect body condition scores on all cows.
- June 6, 2019: All cows placed back on paired treatment pastures.
- September 1, 2019: All cows removed from paired treatment pastures.
- October 1-2, 2019: Forage samples collected at 15 sites in 6 pastures. Measurements included residual dry matter (RDM) outside grazing exclosures to determine quantity of forage harvested. Exclosures reset for year 2 data collection.
- December 12, 2019: Body condition scores collected on all cows prior to breeding.
We collected data on the following parameters in 2019:
- Calves: calf weights at early weaning (March 19) and traditional weaning (May 30).
- Cows: body condition scores (which correlates to subsequent conception rates) at breeding (Dec 2018), early weaning, traditional weaning, and rebreeding (Dec 2019)
- Forage: total forage production (May 2019), forage harvested (May 2019 and October 2019), species richness (May 2019), percent bare ground and invasives (May 2019). Invasives included yellow starthistle, medusahead, and Italian thistle.
|Class||N||Average Weaning Weight||Average Weight (5/30/19)|
|Early Weaned Heifer Calves||21||388||529|
|Early Weaned Steer Calves||21||403||500|
|Traditional Weaned Heifer Calves||19||596|
|Traditional Weaned Steer Calves||23||623|
Cow Body Condition Scores
|Early Weaning||Traditional Weaning|
|Pre-Breeding BCS (Yr 1)||5.0||5.0|
|Early Weaning BCS (Yr 1)||5.1||5.0|
|Traditional Weaning BCS (Yr 1)||6.2||6.4|
|Pre-Breeding BCS (Yr 2)||not analyzed yet||not analyzed yet|
|Total Production||% Harvested||Forage Remaining (June 1)||Species Richness (June 1)||% Bare Ground (June 1)||% Invasives (June 1)||End of Season Forage|
|Early Weaning Pastures (RDM)||2372 lbs/ac||38%||1470 lbs/ac||
5.3 species (grazed)
5.2 species (ungrazed)
4.6 % (ungrazed)
|Traditional Weaning Pastures (RDM)||2224 lbs/ac||51%||1101 lbs/ac||
5.0 species (grazed)
5.6 species (ungrazed)
Precipitation and forage production were slightly above the long-term average for 2018-2019. Even so, we measured differences in forage removal at the end of the growing season and (more importantly) at the beginning of autumn. Cattle producers on California’s annual rangelands typically focus on conserving enough dry forage at the beginning of autumn to carry their grazing operations through until fall germination and the resumption of grass growth. Autumn 2019 presented a key point of analysis; SFREC did not receive germinating rain until late November (making fall dry forage reserves critical).
As expected, the early weaned calves were significantly lighter than the traditional weaned calves. In addition, early weaned calves did not gain as rapidly post-weaning as their non-weaned contemporaries. Cattle managers also noted that the early weaned calves (which were placed on irrigated pasture in April and May) had a much higher incidence of pink eye than the traditional weaned calves (which were grazed with their mothers on annual rangeland during this period). This is an unexpected result and merits further study in year 2.
Finally, as expected, early weaned cows recovered body condition score more rapidly than the traditional weaned cows. This could have bearing on conception rates in years following drought conditions.
Finally, while SFREC did not experience drought conditions in year 1 of this project, several foothill ranchers have contacted the project team to let us know that they did wean early due to loss of fall forage to wildfire. This suggests that there may be additional value to a better understanding of this strategy.
Educational & Outreach Activities
Our initial outreach efforts have included a producer steering committee meeting in October 2018 and a data collection session (body condition scores) in December 2018. The steering committee meeting resulted in a detailed project schedule that represents real-world management conditions for foothill cattle producers.
We presented preliminary results at two field days held at the UC Sierra Foothill Research and Extension Center in 2019.
- Ranching in a Drying Climate: this field day focused on a variety of research into forage productivity and ranch management strategies. Participants included ranchers, extension professionals, university researchers, and agency staff.
- UC Davis Beef Day: this field day focused on a variety of cattle health and management topics. Participants included ranchers, extension professionals, university researchers, and agency staff.
Presentations are attached.